This is really difficult, I would really like to see players on this map in ut99 and I think it would be really popular but would also really like to see you get permission for the release. Maybe give some more time for a response?
If you end up releasing without permission maybe then you would really want to just append -99 to the original title and keep the author in level info but add ported by X-Cell or some such. Obviously, with credit to the original author in the readme. It's a bit of a grey area morally (opinions differ greatly) but not so much legally, I suppose. I don't know if this clearly qualifies as an additional level made from the work or where the real legal boundaries are in this sort of thing.
Personally, I would hope authors of ~20 year old maps/mods would want their creations to continue to be enjoyed today. So, if you want my opinion I would go ahead and give it a full week for a chance on the response then release if nothing is heard. We can always remove the download and map from the server(s) if there is a complaint. It's not as if any money is being made, this is all for the enjoyment of what's left of the players. Other than that, I'll leave it up to you 🙂