See the quoted part below:
That is exactly put. Our company does not allow downtime to happen, but guess what, it still happens. I can report that we had no issues with WHMCS's downtime.
I do think that multiple licensing servers is not a bad idea at all. Sometimes a particular country cannot get internet access outside of that country for some reason (or it is very unreliable), maybe a server in the UK, USA, CANADA, and possible a couple of popular countries that WHMCS services might not be bad.
Hey, even a VPS or a higher end "Shared" host may work.