I'd rather it didn't happen, but it's been common practise for a long time that if a military aircraft enters your airspace, you down it.
Happens reasonably frequently and several times in the Cold War when tensions were even higher. I'm sceptical it'll be WW3 and need to stop thinking showing bollocks against Russia would escalate this way, it's exactly what they're propoganda has been aimed at doing and we need to drop the Kremlin line.