If you are able to refresh rupture 0.2 sec before it expires, the last tick of your previous rupture will be lost and it will start a new timer based on the number of combo points of your new rupture. So there will in fact be a 3.8 sec interval between the last tick of the previous rupture and the first tick of the new rupture. After that it will go on at a regular 2 sec intervals.
Is it worthwhile to refresh it? It depends on reasons why it gets dropped and for how long. Here is an example when it might be worthwhile. Imagine you have 35 energy and you are 0.2 sec away from the time rupture expires.
Case A: eviscerate, with no relentless strikes proc, so you are at 0 energy, 0.2 second later rupture expires, 2.5 seconds later you have enough energy to renew rupture, but you do not have enough combo points. It may take 6 seconds or more before you rupture next time.
Case B: you allow to refresh rupture before it expires. You lose one tick of rupture, but you increase your rupture uptime.
Obvious drawback of allowing to refresh rupture in the simulation is simply that often you cannot refresh it because "a more powerful spell is already active." Other than that, just run the simulation and see for yourself whether it benefits your dps or not to allow for refreshing rupture.
Thanks for clearing that up for me. I'll try and go through scenarios and see what's worthwhile from there.
I also have a quick question of Blood Splatter. Does anybody have a rough idea of how many hat procs/sec that it's worthwhile to pick it up over the 6% eviscerate damage in Aggression, and when it's better to have the 6% eviscerate damage?
I think it's better when you have a much slower combo point flow to have more damage on rupture since you'll be eviscerating less and possibly even using hemorrhage for points when you are getting near capped on energy with little or no combo points, but I'm wondering if there's a specific point that anybody knows when it's better to have and better to skip?
Edit: Edited for grammar/spelling