Why not wait until a script breaks, then fix it and relabel it as OSbot Official? Khal said earlier that scripters have agree to their source being maintained after they leave, so I think this might be a good solution.
I think this would be a better way of doing it than to make all of the scripts from scratch.
I'm not suggesting turning every niche little script into an OSbot official script, but if a big script that many people use breaks and nobody is around to fix it, i see it as an opportunity to create a win for both the old customers, and OSbot.
Another way to deal with this situation completely would be to completely change the way script sales work. Make all scripts a monthly cost, so that people are paying for them as they use them, instead of paying upfront with the expectation that they will be there "forever". But I doubt this would be a very popular solution at all.