The regeneration on the Arcane Armor will remain on the armor and not be limited by level. The design behind this is that having the Orb in your inventory would be a benefit greater than the armor if it would last forever, but by fusing it with the armor you are locking in the stats for the orbs effect for an equipment slot. Will it be viable for 66? More than likely, but using it beyond level 66 you may have to decide if you want to sacrifice stats in order to retain that health regen.
This doesn't guarantee of course that it will always be this way, as circumstances change and we cannot see the future. It's certainly possible we may taper the regeneration many levels from now due to it's power like we did with the Rendtail Ring, but it will always retain some form of regeneration.
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