mass-effect-3
On the system map, I can use the Normandy to scan for interesting items within the system. However, scanning too much draws the ire of the Reapers. They'll chase you back out of the system if this happens.
So far I've always ran like hell. What happens if they catch me? Do I get a game over? Do I lose resources temporarily or permanently? Do I get to fight them (and perhaps gain bonus XP or other benefits?)
No, you can only find war assets and fuel from crashed ships.
This strategy lets you avoid reapers while still giving you lots of time to get your scans done.
Enter into the system you want to scan, scan twice wherever you want to (I try to be systematic but it's up to you). On your third scan the Reapers will appear, so it's helpful to be near the edge of the system. Before you hit that third scan, look at where you would like to reappear (top, bottom, left, right). Scan and move out of the edge of the system bringing up the galaxy map. If you're reasonably good at avoiding Repears you can probably get a few extra scans in before leaving the system.
Remaining inside the ring, point your ship in the direction you want to re-enter the system. For example to show up next to the Mass Relay you would point your ship right.
You will re-enter far enough away from the reapers to perform more scanning. Repeat this technique until you've completed your scanning. Note that the reapers don't move closer to you while you are examining a planet/etc so you do have time to land and get your probes launched.
This video demonstrates the technique effectively.
Best Answer
You get a critical mission failure and have to choose to exit, load or resume/"try again"-just like if you died on a mission.