Marv; Interesting questions you have posed. Not being very knowledgeable about most other gaming juristictions outside of Atlantic City, I can say with much confidence that to the best of my knowledge, no Silver Strike machines that have been removed from any casino floor in A.C. have ever been brought back. I do confess that I refer to the silver strike tokens that are no longer available as "obsolete".
As for your question regarding chips ... I believe that ANY chip that has been issued in Atlantic City from a property that is presently open can still be redeemed. Excluding plaques, I know of NO "live" A.C. chip issued by a casino that is presently open that has been devalued, or not redeemable for its face value. That's not to say that an "obsolete" chip placed on a gaming table as a wager by a player, won't be replaced by the dealer with a current rack chip ... but the bet would be honored .... and the chip would in all probability be put into the rear of the rack so as not to pay it out to a winning wager later on. Even Brighton chips would still be accepted at Sands if presented for payment.... and I'm fairly certain that The Grand chips would still be honored at Hilton, and the original Hilton chips would still be accepted at Trump Marina.