Yes, the fruit will mature, but if the branches are damaged it may not swell up and be juicy enough to be of the best quality. However, it'll still be lovely as stewed fruit or jam. If there's no damage to the branches they too will be ok to leave on, but it might be sensible to reduce them by a third or so, to lighten the load and protect against the same problem in subsequent years. Pruning plums, if it has to be done, is a summer months' task.