Just a bit from my own experience. Coil failures on relays do occur but I've had a lot more failures from the contacts - 10 A contacts switching logic signals is the big one that comes to mind. The contacts eventually carbon up and will not pass the signal when they are closed.
If you are using a relay to transmit a logic/low current signal (as I've inferred from your post), you might want to consider gold cross-point contacts on your relay. They are rather expensive and not available on all relays but, for those few times you are using a relay in these situations, they work well.
If you are using a relay to transmit a logic/low current signal (as I've inferred from your post), you might want to consider gold cross-point contacts on your relay. They are rather expensive and not available on all relays but, for those few times you are using a relay in these situations, they work well.