At least this chapter actually referenced something from early on in the series, if
! Tousen was actually beaten: breaking a hollow's mask is a one-hit kill, at least for those who are completely hollows and not hybrids between hollows and shinigami. Arrancars normally are, but I'm pretty sure that Ressurecion returns them to their original form (or, in Aizen and company's case, turns them into Hollows). If Tousen was actually killed by that, it means that transforming completely into a hollow made it so he gave himself a ridiculously huge and really obvious weak point.