They'll VERY likely be fine, and would be fine if they did nothing at all instead of ineffective or even harmful "alternative remedies". The reason COVID is such a bitch is that everyone gets it, so even if deaths are under a single percent of people infected that's millions of deaths. Add in all the seriously affected people who survive but need expensive/labor-intensive/lengthy medical care and you can see why it's a big deal.

These folks can get away with anecdotes about their horseshit saving them because COVID was unlikely to kill most of them anyways. They are, however, more likely to be more seriously ill for a longer period of time with worse "long COVID" symptoms. "They found initially and during recovery from symptomatic COVID-19, fully vaccinated participants had lower concentrations of inflammatory markers than unvaccinated participants, suggesting vaccination is associated with short-term and long-term reduction in inflammation, which could in part, explain the reduced disease severity, mortality and risk of long COVID in vaccinated individuals."

Vaccination is at least as much about shorter, less severe illness with less likelihood of long-term effects for survivors as it is about preventing death. So the Ivermectin user will probably survive (and thus will likely claim they never needed the vaccine), but they and the roommate will have a harder time of it than they would have otherwise both during and after infection.