At 200K you'd have to have maintained the car really well for it to be reliable enough for a 900 mile round trip. If you want to do the trip and some maintenance is behind schedule, this could be the incentive to get it done though. If I were going on such a trip w/my 200K Corolla, here's what I'd do before leaving:
- Change engine oil and filter
- Proper transmissions service, for auto's usually means to drop & clean pan, sieve fluid for unusual debris, replace filter.
- Fix all leaks
- Hand spin water pump, alternator, AC compressor, and radiator fan, listening for abnormal sounds or play in the bearings. Any coolant in water pump weep hole, if so replace water pump.
- Rebuild or replace both side's half-shaft CV joints and replace all 4 boots.
- Replace spark plugs, wires, cap, and rotor
- Check valve clearances
- Engine and transmission mounts ok?
- Suspension bushings look ok?
- Tires less than 3 years old and in good shape? Any abnormal wear patterns must be explained.
- Visual inspection of brakes, at least one wheel front and back. Check wheel bearings at same time.
- Any fluids low? A reason must be found.
- Any unexplained noises, clunks, whines, whirs, etc must be explained or fixed.
- Any Starter, Battery, Charging system problems? Have it all tested.
Ask you shop to recommend any hard to find (for you car) repair items it would make sense to bring along in the trunk. Alternator, starter motor, water pump comes to mind.
When I'm presented with this issue, I rent a car. It's usually pretty inexpensive if you book well in advance.