The letter of copyright law might allow a prohibition of forking and relicensing (to reiterate, the TC author would have to reveal him or herself in order to enforce that prohibition), but philosophically...

"I don't feel that forking truecrypt would be a good idea..."

This is a straight-up abuse of copyright law. Author has no intent of profiting from the project, no intent of continuing to work on the project, and still waves around the hammer of copyright as if it's a fundamental right absent any connection to the constitutional qualification of promoting progress in the sciences and useful arts.

To say there's a moral imperative against forking and relicensing in this scenario is stretching the rationale for the copyright monopoly quite far.