I think it's safe to assume that the 5th Imperium is working really hard to find some way to stop the bio-weapon, and that all efforts to reclaim found 4th Empire technology have "make sure you don't bring back the bio-weapon" as pretty much the Prime Directive.
Given the bio-weapon's self destructive nature, there can't be much of it left even in stasis, particularly since stasis is not self-sustaining and nearly all stasis capsules have long since collapsed and released any bio-weapon contamination to die out soon afterward.
When you add in the safety mechanisms installed on matter transmitters, saying the 5th Imperium is "living on borrowed time" is a gross exaggeration. There is very likely no viable bio-weapon left to release, and if there is any left, it is certainly only in a tiny number of potential remaining sources. Then those sources have to not be handled safely and the infection has to find its way through the 5th Empire's anti-bio-weapon defenses.
Doesn't mean it couldn't make a good story, of course. Stories are written when the colossally unlikely becomes real. But it's certainly not some sort of ticking time-bomb unless RFC wants it to be.
