With a VPI 16.5, these things have been around forever - and probably will be for some time more. There's not a lot going on inside the box, so unless you use the thing exceptionally hard or frequently, it should give you a lifetime of use. Don't think VPI is going to disappear anytime soon either, but if you're really paranoid, stock up on the replacement tube with felt things. Nothing else - including perhaps even some kind of DIY for the tube w/ the felt - can't be sourced somewhere else if necessary.
So I guess what I'm saying is that if this is a MAJOR concern for you, the VPI 16.5 is probably the least expensive & safest bet.