Do you not agree that if the entrepreneur took the deal, it would kill his company? If so, a kill, in shark language, is appropriately described by eaten alive.
Now, actually deciding to replace the active codebase with something that's terrible could kill his company, but that's down the road a bit.
Rewrite the site from scratch. No more technical resources. Sounds like a pretty good startup-killer to me.
I agree the 10% part is not the problem. It's the strategic change of direction into a dead-end that is.
Just asking for clarification here... Honestly sounds like a What The (Cluster) Fuck in the making...
When it looks too good (or too suspicious) to be true, it probably is.