Actually, that's not a bad idea since Jon Culshaw really does have a long standing interest in astronomy so him fronting the show would probably help to ensure that the Sky at Night wasn't dumbed down into inanity and moron-ness
That said, it's perhaps more likely that either Chris Lintott or Brian May would take over the main presenter role although I hope that Jon Culshaw can still make appearances from time to time.
I've kept a look out for news articles about the BBC cancelling the Sky at Night but, fortunately, nothing's turned up and the main Sky at Night presenters and guests haven't mentioned anything in their twitter feeds either so I think it's going to continue. As a short monthly programme, it can't be that expensive to produce anyway.
Finally, here's one of Sir Patrick's own favourite sketches - enjoy
I agree it would be nice to keep all the existing presenters, but we don't want to saddle the new production with Patrick's baggage. Sometimes a fresh start is required, although NOT at the expense of dumbing down trying to (incorrectly) appeal to the youth by employing celebs.
They shouldn't be even considering cancelling the show , if anything they should be increasing the output. Take for instance "stargazing live". Why ever not "the sky at night live" (I know its a independent production company). The BBC could have market the SoN to something more than a late night monthly show, make it a franchise.