I can only speak to what was typically done in the past. When I was there, if you were a customer in good standing, then we replaced the key at minimal cost. Like $100 or $150 bucks or so. Now, that was dependent on a few things:
1) You could not have recently lost another key.
2) You had given a real "good faith" effort to find it. I think they often quoted the "multiple license discount" cost to replace the key at first to encourage folks to really, really look for it. Because if we made it too easy to replace, then it wasn't worth their time to genuinely make sure it wasn't lost.
3) There weren't any "red flags" in your customer file. Like maybe there was dispute between you and a previous partner over who should really own the key. et cetera.
4) You're current with your "maintenance" payments. If not, then they'd back charge you to get current.
This is pure speculation, but I have a feeling the new RISA/Nemetshek will probably tell you that they don't have any keys anymore. That's probably not true, but may be close enough to true for them to feel comfortable with the lie. Even if it were true, it's almost certainly possible for them to get more keys from Sentinel / Gemalto. Though I think the cost went up significantly. If they order only a few keys at a time it might be $400 per key or something really significant like that.
I'd also guess they'd offer to give you six months or a year's worth of "subscription" licensing for free. That's the more profitable revenue stream for them. So, there's lots of incentive for them to push customers in that direction. At the worst, they'd probably give you 30 or 60 days of subscription, just to give you time to search for the key.