If the current rents actually keep the house maintained over time, and if you are more focused on housing security than on making a profit, you could consider creating a cooperative (if allowed under local law, and would be lots of paperwork and possibly legal fees).
Seems like it is likely a big regulatory project and/or legal challenge, but if the price is right and it makes your lifestyle sing, go for it.
Based on what you've shared, it sounds like the current use is probably not legal (imo there's virtually no way that 11th unit counts as a unit!).
This suggests the owner will be unlikely to be able to sell for much $ to anyone without an emotional tie to the building - unless it's worth it as a tear-down. So you might have time to brainstorm.
If the current underlying zoning allows SRO or rooming house use, that probably makes legalizing the layout possible (still might require a lot of fire safety retrofitting...)
If the current zoning doesn't allow SRO or rooming house use (some do, but not many), count up the kitchens and that may be the highest likely unit count, assuming you're willing/able/allowed to bring up to current code...You could get creative with "congregate housing" to meet the letter of the law (IF layout allows...) - at a minimum, everyone would need access to a full kitchen (at least technically), and unit separation would need to make sense. Since local zoning is quite particular, find someone who knows. And be willing to read the entire relevant parts of the zoning and building codes, sometimes there are elements even the building or planning dept doesn't know or hasn't seen used enough to remember. Or, depending on sf minimums and budget, you might be able to increase the unit count by installing "full" (a kitchen sink and a range, where we live) kitchens in some additional units...