It's hard to say, because many people double dip with minoxidil and Finasteride, including myself, so giving you an account of my results would mean that I am describing the drugs' efficacy as a combo, rather than what minoxidil-only would do.
That being said, I was off Finasteride for about 9-10 months and stayed on a minoxidil-only (5%) regimen, using it once a day during that period of time. I kept losing a little density over time between months 3 and 10, but I mostly maintained my-then gains on minoxidil. No doubt I would have lost more had I stayed off finasteride longer. (Started seeing a difference by month 3-4, going from no shedding to lots of hair everywhere). I might have also lost less during that time if I did minoxidil twice a day, but anyway, it's a slow but steady decay, if you have already achieved results.
Most of my regrowth results are from minoxidil - I went from a Norwood 3.5V or a NW4V to a little thin Norwood 1.5~, and I was on finasteride only for nearly a year before getting on minoxidil, after which point I got those results when I added minoxidil - so I know (most of) the regrowth is from minoxidil. But that being said, it's the finasteride that makes me maintain and thus enables minoxidil to do its work without any decay so to speak - and I know this because I kept losing ground when I was off finasteride for that 9-10 months or so.
So yeah, even if you did get gains on minoxidil, it might be more or less offset by the hair loss that keeps on going - if not offset to such a degree that you just keep losing even with the regrowth you might be getting, as even with any regrowth, the fundamental balding process is not stopped, unlike if you're on an anti-androgen. Now that I am back to finasteride, I can tell you that the shedding has come to a complete halt (whether it be hairs on the pillow, or in the shower, etc), so I'm likely to bounce back up with minoxidil.
That being said, I haven't found any decay in minoxidil results (relating to its efficacy over time), aside from losing ground when I temporarily stopped finasteride - and I have been on minoxidil for 2+ years.
So, TL;DR: consider getting on finasteride? Good luck.