Let's say that they run no more ads at all, and get no more signups.
If we assume 10-20% of the current waitlist customers convert to paid (industry standard) then that's 20-40 customers.
Oh and let's be conservative and say each customer is only on the lowest tier of $27/month.
That comes out to a projected monthly gross revenue of $540-$1080.
And a yearly revenue of $6480 - $12,960!
Not bad for a few months of work.