Worldbuilding speculation: I wonder if any mages have attempted to 'keep' spirits safe in their own havens. In this scenario, Onni would build a virtual cabin or such for Tuuri to 'live' in, within his virtual Finland.
That could be possible, but I suspect it wouldn't work out very well. Finnish mages are supposed to guide spirits on their way, keeping one around for selfish reasons could be a violation of everything Onni's meant to do, and that could have bad consequences for them both.
We've seen what happens when a spirit is trapped in the real world, having one trapped in the spirit world could be just as bad.
Of course if Tuuri
wants to hang around she could end up like Pastor A. Still there but slowly losing her memories and sense of self.