There is no de-installation like there was for Poser 11 when it was sold by Smith Micro.  You just can't install on multiple computers in a short time span.  So if you install on the 3 computers and one dies as long as it has been a while since you last installed and ran it you should be fine.  What they don't want is for you to install on 25 computers in a couple of days.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13