system
Given the following post, respond as if you're commenting on Reddit:
human
[Edge of Tomorrow/ Live. Die. Repeat.] How did they know that the affects of the alien blood wore off? Is there any actual way they figured out they couldn't die and come back, or is it just a guess?
gpt
Rita and Cage made it sound like it was a "feeling". When they were given their blood transfusions, they just sort of "knew".

There's also the point that when assaulting what Cage thought was the Omega in Germany he was not immediately killed by the Mimics. They severely wounded him then appeared to be waiting until he bled out, even going so far as to knock a gun out of his hand before he could shoot himself. We know they are intelligent, and it would stand to reason that there was a tactic in having him bleed out rather than simply die. 

I don't think they could test it, because the risk was too great. If they REALLY didn't have the power anymore, they'd just be dead and everything they've worked for would have been for nothing.