Why is the 501st hunting down mercs with an indefinite-capable force user when they should be hunting down Jedi MASTERS that escaped the purge? The 501st is elite and relatively small in number, they can't be everywhere at once, or even close to it. Unless the group has personally pissed off Vader, there are many more priority targets elsewhere. Throw some other legion that is of lesser competence, not the cream of the crop.

Once you remove the "best of the best is hunting us down" pressure, many of the potential survival plans become more viable. Infiltrating regulars and conscripts isn't particularly difficult if they can simply find and kill some storm troopers. Disguising their identity as some other random mercs that definitely didn't blow up an imperial cruiser is easier this way.

Make up some lost legend or ancient/hidden civilization on toxic hellhole #12 that makes the idea of hiding there not only more plausible but interesting as well, with potential plot hooks.