It'll make for an interesting by-election. Locally the CLP has been in real trouble for a while, with the CLP being suspended due to allegations of bullying last summer. And, no, nothing to do with Corbyn, just different groups jostling for position to replace an MP who was obviously not going to continue forever.
Considering the national picture, it'll be most interesting to see how the Lib Dems fare. This'll be a test of whether there's a revival going on. The Lib Dems had been a steady second in the constituency since the mid 90s, but got hammered in 2015, losing 10,000 votes and falling to 5th. If they're going to see a national revival any time soon, this is the kind of seat they need to show progress in. Not to win, they wont, but to at least get back to second place.
Labour will take some flak if their majority falls, which it probably will, but being falsely inflated at the last election makes that inevitable. If they get a bit over 60% of the vote, that'll be a decent result and put it back to where it usually is. If they get below 50%, they should worry. A loss is all but impossible.