Do't know if this suggestion helps because in my case, I was patching a hole that I was then going to cover with other flooring, but I had that situation where about half a tile broke off and disappeared (long before I lived here).
I pasted over the hole with something called "Patch-it" (I think that's the name). It was in the same section as the spackle. I was a really stinky rubbery spackle-type stuff that dries in an easily removable fashion later on. It really just crumbles back away when you make an effort to dig it out. With a little extra elbow grease you could certainly remove it cleanly when the need arose.
Maybe you could do that and then cover it with one of those 1 1/2 or
2-inch flooring transition strip -- either the uneven (thicker on one side than the other like for carpet) or a completely level one that works for transitioning between two different but level flooring surfaced. (Sorry for my horrible terminology on the "flooring transition strip;" it probably has a better name than that, but I'm nor sure what it is!)