The best thing to do is diagnose the problem first. If the dash lights are out when the car stalls there is a good chance it's the ignition switch. Just because the switch has been replaced doesn't mean that it doesn't need replacing again. Over time the ignition switches wear out. One of the things that I do to check the ignition switch is to wiggle it while it's running to see if the car stalls while the key is in the on position. If so, and the dash lights are out then try replacing the switch first to see if it takes care of your problem. When a main relay fails it usually takes some time to stall and doesn't want to restart right away. I don't see a lot of issues with ignition coils, and while I'm sure in extreme cases and O2 has caused stalling, I've never seen it. A stuck open EGR would cause stalling, but if it's clogged it won't work and won't make the engine stall.