If the worst should happen here’s some dos and don’t:
Don’t panic!
Do save all the little bits of wood which have come adrift and are now all over the floor.
Do slacken the strings immediately.
Don’t try and fit the two pieces back together. There may only be one chance of getting this right.
Do loosely wrap the whole lot up in a paper bag or bubble wrap. Don’t use fabric or cloth as it will catch on the splinters.
Don’t leave it for a week before taking it to a repairer. All those loose wood fibres are getting snagged and torn, and are making the repair much harder.
Don’t have a go at repairing it yourself using pva, uhu, pritt stick or superglue. The repairer you take it to, once you’ve failed, will lay a terrible curse upon you. Fact.