I've not heard of a tape being too far gone for baking, but I suppose that's possible if it's been used a lot in its sticky state or been otherwise mishandled. Degauss the tape after baking.
I've kept all my old tapes after baking them. However, acorec makes a good point and you should be very cautious with old tapes because they will eventually revert back to the sticky state... well, maybe.
Unfortunately, it's not really predictable to any certainty how long a baked tape will maintain its integrity. It depends on the tape and environmental factors, which will vary from brand-to-brand, tape-to-tape, and place-to-place.
For example if you're in Louisiana where you can cut the air with a knife in the Summer time your chances of keeping a baked tape usable for long is pretty bleak. On the other hand, if you're in Arizona you may not have to bake the tape again.
If kept in an airtight plastic bag (use large zip-lock bags) in a climate-controlled environment some tapes may never need baking again, but your mileage may vary.
That being said, as for having blank tape on hand it's really not worth the hassle and the risk to your equipment. I strongly recommend buying newer Ampex/Quantegy tape (made in 1994 or later).
Secondly, I wish everyone would stop buying ancient used tape of questionable quality on eBay and such for this reason -- we only have one maker of open reel tape left on earth, Quantegy (ok there's Zonal in the UK), so we better let them know there is a demand for new tape or we may lose them as well.
If you do buy Ampex tape on eBay, ask the seller what the date code is on the label. If he won't or can't tell you then don't buy it. If it is older than 1994 you should pass and keep looking. All tape marked Quantegy is ok.
The bottom line is that sticky tape shed sucks and it will take more than a routine cleaning of your machine if it has a run-in with it.