My network is designed such that I originate our master prefix at several of our access-layer routers into OSPF. This way, unused space gets sunk immediately. Then the border routers only have the network statements to match the /20 block prefix, but no "nailed up static null route" on the border routers themselves.
This way, if the border router is active, and has an active link to its eBGP peer(s), but is isolated from the rest of the ASN for some reason (failed optic on the inward-facing links, for instance), then it will withdraw its advertisements of our IP blocks (as well as any longer-prefix sub-sets of these being announced for traffic engineering purposes).
Our DFZ is not large enough to completely mandate that we deploy RR hosts yet - but when I do, it's going to be the RR where I advertise the nail-up prefixes, and that will be directly into iBGP. The next hop of these nail-up prefixes will be to some /32 that I designate as a recursive route pointing at Null0 (we use Cisco for our core - sorry, Mikrotik) so that every router will know to black hole the master prefixes locally. If some border router cannot reach the RR, then that means it (the border router) is isolated from our core, so it will drop the prefixes by virtue of losing the iBGP session. (I'll experiment with this to decide whether I would rather continue using OSPF to propagate the route from the RR to the border routers for convergence time reasons)
When given a spoon,
you should not cling to your fork.
The soup will get cold.