This is already the case, confirmed it in the admin chat a couple months ago. Just be careful to not fuck it up.
Pretty sure this is already treated this way; same as saying "hands up or die" and having the dude double tap tab and run away.
IMO this shouldn't be added. The titan is one of the strongest weapons in the game and is balanced by the carrier having to explicitly engage it in most scenarios.
Also:
> Shoot at medic ground unit in rebel
> Wait for him to fly off
> Kill his heli lul
It does feel kinda weird to have to engage someone taking your own vehicle when in this situation, but I don't think it should be added for the same reason as above.