UCaaS and hosted PBX often look the same from the outside. They are not. A Microsoft-led or vendor-led UCaaS shop is a different sale to a traditional VoIP reseller. The buyer will unpick the invoice in their head either way.
What they can take on is the customer list, the licence position, and whoever still knows how the call flows were built. If that knowledge is only in your head, say so in the first conversation.