Not the greatest of options, but if you have a summoner in your FC, run the instance with them. Should things go bad, they can toss out a few Physics to keep people up till your lag spike subsides and you can get back on it. In addition, they get a raise so should you die mid fight, they can get you back up. Lastly, don't be afraid to use the limit break to save the group. If you come back from a lag spike and several people are low on health, it is an easy way to bring everyone back.

None of these will save you in later harder fights, but it should be enough to get you through.