You can forget about the back emf from a relay destroying the windings. Prior to the semiconductor era there must have been literally millions of relays experiencing immediate switch-off, and hence self induced back-emf, without self-destructing. We are often guilty of looking for problems where no problems exist.
If your system relies upon the relays being powered to trigger your camera (or whatever) is it relevant how long they take to de-energise once the trigger voltage is removed.
A simple low value resistor, say 10 ohms or less will probably be sufficient to minimise hold-up time, but it will be a balance between decay time versus back emf.