Seems to me like rational thinking has gone out of the window at the first mention of the dreaded "S" word!
Based on what LAX has said, MAN and Hainan were at the handshake stage for MAN flights, suggesting that both sides believe that a profitable service is viable. Someone has then heard Hainan were looking at LGW in addition to MAN. 'Hold on' they said, 'if you send those flights to STN instead of LGW we can improve the deal we have already agreed even further'. 'That interests us' said Hainan, 'we'll have some negotiating to do to sort out permissions for the STN end, so we'll hold off announcing the MAN flights until we know if STN is going ahead. Bigger headlines if we can announce 2 destinations at the same time. It's 7 months before we plan to launch MAN, so hanging on for a few weeks isn't going to make significant difference'.
If the announcement hasn't happened by the end of the year (which would still give 5 months ahead of the start date) then I might start to get concerned, but 7 months? Get real!
Further down the line if the profitability of either route isn't working out as well as they hoped, then I'm sure Hainan would use the fact that increasing airport charges if they dropped one of STN or MAN would place the other one in jeopardy as a negotiating point.
To my mind the biggest potential fly in the ointment is if Air China decide they want the MAN-PEK route for themselves, and Chinese politics dictates that their wishes supercede Hainan's wishes.