So basically, if F2pool really moves out of the agreement and one - even small - pool joins them, then Segwit2x will have already a hard time.
i wouldn't count on F2pool and what they say they do. they will change their mind at any time as they please.
You may be right. But even if they continue to support Segwit2x for a while after the fork date: I suppose that F2Pool could be one of the first pools to retract its decision if anything does not seem to go well.
I think they are a strictly profit-oriented pool without any ("big" or "small blocker") ideology - so if e.g. a smaller pool switches back to Core and enables "usable" block times (significantly less than one hour) again, or if BitPay and Coinbase turn to support again the Core chain fully, then Wang Chun could rapidly change back to the good ol' Bitcoin Core chain.
That may be also valid for other not-Bigblocker pools - they could switch back on the first sign that the Core chain could be the most profitable.