failure rate of automotive 30a relay?

Typically when a relay fails it is the contacts that go bad - this is especially true if you are switching the fuel pump under load (or any other big load).  Switching the relay on and off while power is applied causes the contacts to arc - eventually wearing them out.

Relays are typically designed to withstand 1,000,000 switching cycles under full load.  In a car, you will most likely never switch that many cycles.  You can pull up some datasheets for 30A automotive relays on digikey.com if you know how to search correctly.

The best advice I can give you is to just keep an extra few relays in the glovebox.  Use high quality sockets and if you ever have a problem starting the car you can try swapping out the relays.  Better yet, you could make some jumper wires to install in the sockets to bypass the relays all together in the case of emergency.  Of course, this backup plan could severely limit the overall security of the vehicle, but a sacrifice will have to be made somewhere.