Transferring old metal particle Hi8 tapes Recently I was playing a Hi8 tape from 1998, when I tried rewinding and rewatching a part (stopping the tape, before rewinding).  The part of the tape I had just watched was highly distorted and black and white.

So, I've learned the hard way that old metal particle tapes are prone to being erased, when watched.  Presumably, the 'MP' on the tapes stands for metal particle?  These tapes have been stored in a safe place.  How many years before this problem arises with MP tapes?

Is there a better alternative than playing these tapes into a capture card?  If not, I realize that I only have one chance to capture this video.  If this is the only option, I'll expect to capture until the read head becomes too affected by residue, and then stop and clean the head, and repeat.  Any advice would be appreciated.
You do need to play the tapes onto a capture card, yes. And the sooner the better. You don't just get one attempt, but you will get a slight degradation of quality every play, so you are best off aiming to do it in one pass if possible.

I recently captured about 50 tapes from the late 80's to the mid 90's and I did about half of them then cleaned the head then did the other half. Degradation wasn't noticeable, but I just thought I should do it just in case.

As to how long you can store them - is the safe place shielded from EMF, heat and humidity, then they can last for years, but due to the nature of magnetic tape, the magnetic field strength of particles affects adjacent particles, so quality will degrade no matter what.

When configuring your capture, set it for the highest quality you can afford - as there are utilities which can clean up some noise and speckle once the signal is digitised.