@fashionables I'm a parent of a DD at a GDST junior school (lurking on here to get a sense of what awaits us for 11+!)
I had been worried about teachers leaving too, but given the fact that over 70% of independent schools have already rejected the TPS, I'm not sure where all the striking teachers think they're going to get jobs elsewhere with better pension schemes. (I should say, I'm in favour of the teachers getting decent pensions, and supported the strike, but the view amongst most GDST parents I know is that the offer now on the table is a pretty good one. And my understanding is that a lot of GDST teachers have accepted it already and are back at work).
PHS have definitely been one of the most politically active schools during the strikes (with a lot of teachers on the picket line) so I totally understand your concerns. But I think the fears about there being a drain on good teachers within the Trust schools is perhaps being a bit exaggerated - as I say, in order to leave, they'd be seeking a better pension offer elsewhere and I'm not sure they're going to find it.