Dear Qurious, for all practical and experimentally testable purposes, the measurement theory was understood in the late mid 1920s, soon after quantum mechanics was discovered, and the "measurement problem" was solved at the level of phenomenology. The old interpretation of quantum mechanics left some questions open but from an empirical viewpoint, they were "academic questions" only.
Later progress, especially the derivations of decoherence in the 1980s, has confirmed the Copenhagen picture and derived the classical-quantum boundary, a missing piece in the old Copenhagen approach, from the rules of many-body quantum mechanics itself. All problems related to the measurement theory have been answered in principle.
People may prefer different philosophies to interpret quantum mechanics - consistent histories; many worlds; the old positivist Copenhagen interpretation - but they ultimately agree about the predictions for all experiments so their philosophies are physically equivalent. What's important is that the predictions may be made for every situation now.
So the measurement problem can't be solved by quantum field theory, string theory, or anything else, because it has been solved for a long time before these newer layers of physical knowledge started to be studied.
Quantum field theory, string theory, theories describing states of condensed matter physics, nuclear physics, atomic and molecular physics, optics, and other subdisciplines of physics that depend on the quantum phenomena take the universal postulates of quantum mechanics as exactly valid principles that cannot be modified in any way.
Modern developments in the research of entanglement, original started by Einstein and his collaborators (especially Bell's inequalities, GHZM state, and Hardy's paradox), have eliminated all doubts that the new quantum description of the reality has to be taken seriously and all "classical" models of the quantum phenomena may be falsified.
So string theory - and even quantum field theory - don't change anything whatsoever about the shared framework of quantum mechanics and its postulates. The question whether our Universe follows the known laws of quantum mechanics has been answered, de facto for 85 years, and most likely, nothing will ever change about these basic matters again.
There is no real problem over here and the postulates of the quantum dynamical framework below will stay with us.
- The world is associated with a Hilbert space
- Every complex linear superposition of two allowed vectors is allowed
- Every observable is associated with a linear Hermitean operator
- The squared absolute values of probability amplitudes - complex inner products with eigenvectors of the observables - determine the probabilities that one or another result will be observed
- Nothing except for the probabilities may be predicted; it is incorrect to imagine that any physical system that could be affected by quantum mechanics has any well-defined, determined properties (variable quantities) prior to the measurement
- Evolution is encoded in the Hamiltonian or the action, via the Schrödinger's equation, Heisenberg equations of motion for the operators, Feynman's path integral, or another equivalent mathematical formalism
What quantum field theory and string theory are doing is to find and investigate the more correct Hilbert spaces and the "Hamiltonians" (or equivalent structures) acting on them that define the dynamics. There are also people who study theories based on the basic assumption of "denial of quantum mechanics" but they have nothing to do with research in particle physics or string theory.
Of course, it is hypothetically conceivable that sometime in the future, one (or several) of the postulates will be falsified experimentally. If that occurs, quantum field theories, string theory, and many other theories in nuclear, condensed matter, and other branches of physics will be showed invalid or incomplete, too. But the "fear" that this could happen doesn't mean that science shouldn't build on the assumptions that seem to be valid according to the current state of the art. If the "fear" were enough to stop research, science would become impossible.
There is nothing "premature" about taking the principles of quantum mechanics as established facts, especially because they have been known for 85 years and every single experiment that has been done in those 85 years has confirmed that they are correct.
In his excellent 1994 talk Quantum Mechanics In Your Face, eminent physicist Sidney Coleman compared the resistance to quantum mechanics to the resistance to the heliocentric theory. People used to say that the geocentric beliefs (much like the belief that the world has to be classical) existed because it "looks like" the world is geocentric (or classical). How would it look like if the world were heliocentric (or quantum)? Well, it would look like the real world. Welcome home. By the way, Coleman's talk was given 17 years ago but most people still haven't accepted quantum mechanics as a fact.