How to calculate total chance from different simultaneous chances

so impale on 2 targets already has a better chance to heal (albeit less) thanks a lot for the help, gotta love math. (not sarcasm) gotta save this page for the large formula though.

As for how much you'll heal, on average, it gets even more simple:
Chance of success * amount healed
amount healed = damage done * percent heal
So you have 5%*5%*X, where X is just... add up all the hits from your attack. If my DrK is doing about 30k * 12 with Buster, then it averages 900 hp healed per attack - of course the actual distribution of the healing depends how many hits succeed a particular time. But in the long run on average it works out.

From there you can figure out how fast you're healing per second, and decide what the max mob damage you can go to without burning pots is.