Question No. 1:A new haed gasket will hold at least as long as the first one did. 100 to 150,000mi. is the normal life of this gasket.
Question No. 2: Nothing in term of preventive maintenance or nothing you can do to prevent it from happening again. The driver/owner is not the cause of the failure, except if you overheat the engine.
Question 3: Make the trip: Maybe yes (probably), maybe no. Impossible to tell. If I was temporarily tied-up for cash (I'm not temporarily tight on cash, I am permanantly tight on cash), I'd go on the trip and closely watch the collant temp. gauge. Life is a risk........
If you have the job done, you should inquire about the valve guides. If you car is using oil, it would be the perfect time to fix that problem at the same time. If you postpone this repair, the same labour cost will be incured if you have the valve guides done later.
Best of luck