I fiddled around with it a small amount just to see if simmering frenzy could be sustained indefinitely on a stamina nightblade.
frenzy being just about the only thing stamina could use after all.
I found that in the case of 2h/ bow nightblade the answer is it's incredibly easy.
simmering frenzy stacks your weapon damage high which feeds into high vigor tooltip and something like rally easily heals you to full at a single button press.
you still have leeching strike and merciless resolves to heal as well so pew pew to victory was funny.
pve overland mobs were getting hit with like 50k+ snipes and super fun,
I did not test in battle spirit -60% healing though for pvp. but for small windows I'm sure some nasty combos will reveal themselves