I think the key thing about the split is that it prevented castellano from making a move on dellacroce's man gotti until he had proof in the form of ruggerio's wiretap tapes.
If it weren't for the split with dellacroce commanding, basically, his own family then castellano probably would have had gotti's people hit a lot sooner and with a lot less proof. The presence of dellacroce made the situation a lot more political. That's why castellano kept asking for the tapes and dellacroce would then tell gotti that he can't keep stalling him and it's going to be bad when he does get them

DeMeo got away with a lot, nino never really had any control over him. It took half a year and a dead vaccuum salesman before nino finally got roy to kill his man chris for killing those cubans.

As far as gotti is concerned, I don't think killing roy mattered much because while he had the name, the gambino's still had the gemini twins running that crew and they were just as dangerous as roy was.