Just one data point, but my wife and I recently (end of September) flew EDI-LHR-LJU (Ljubljana) with an overnight stay in the LHR going out and on the return home.
in both cases we had checked baggage that stayed in T5 overnight and it made it fine onto our flights the next morning.
This was a little stressful on the way out, as it was a cycling holiday and it was our bikes. No bikes, no holiday!
Obviously **** happens now and again, but you're more than likely to be absolutely fine