I'll do my best to clarify the options which you have.
To make sure I did get the proposed scenario correctly, let me re-phrase your question a bit, should I have missed a point, please do let me know.
You are generally planning to use some of your very own recordings (not including any remixed ads),
which you have already shared on wikiloops in the past.
And you are wondering whether it is necessary or possible to remove tracks which you have shared on wikiloops before making use of these tracks in a different context.
So, can you use your own recordings for anything, including commercial use after having published them on wikiloops?
Yes, you can, since you have not given up on your rights to do so, BUT: You may no longer claim that you are the exclusive rights holder.
From what I have understood, this may not matter for your plan - if you would like to license these tracks to someone for some money, that's your right to do, just don't tell anyone "nobody but you will ever be allowed to use this track", because that exclusiveness is no longer available.
Now, is it possible to revert this "lost exclusiveness"-status by removing tracks from wikiloops?
No, that is not possible. wikiloops could theoretically confirm to you that no usage of your track will happen on wikiloops after you have removed it, but since there is a high chance that some private user got hold of the track you offered via wikiloops, that individual does have the right to continue using your track for anything covered by the granted license.
Mind, this legal situation starts the very moment you click on "publish", it is not tied to the question of "has the track been downloaded or remixed?".
You have to keep in mind anyone could record the track off the browser instead of downloading it, make a screenshot of the track on wikiloops and the license and proof the legit use of the track that way, there is no way to recover the exclusive status.
Sure, one may argue a track that has no downloads, no remixes and less than a 100 listeners has a very low chance of turning up anywhere in the future, so one might consider offering it as "unpublished" to some other party... but that can go wrong very very badly, and music publishing history is full of legal battles about exclusivity. Personally, I'd be very cautious and rather not risk anything like that when getting into dealing with 3rd parties.
So, which tracks can be removed from wikiloops?
As you noticed, you may remove any track that has not been remixed yet, and it will no longer be available on wikiloops after that.
If tracks do have remixes, you may no longer remove them, simply because that would leave the remixes without an origin, breaking the whole idea of the wikiloops remix tree. To keep the wiki-structure of wikiloops, the attached remixes would have to disappear once the root track they started out from gets removed - and that would certainly annoy anyone who took time to record a remix.
Again, this may seem a strange rule at first, but if you acknowledge that there are some tracks that have grown way over one hundred remixes in various branches, you'll understand why there is an interest the remix tree cant be easily destroyed by a single users decision.
Now, if some of the tracks you would like to remove may have only a small number of remixes, and depending on how well connected you are to the creators of these remixes, you are free to ask them to remove their remixes, until your track doesn't have any remixes attached and become free to remove. That does take a little effort, but it has been handled like this in the past, too, whenever someone felt a need to remove some already remixed track.
The only time we have had to "chop down" entire remix trees is when some track turns out to be a copyright fraud, just to give a full tour of what may happen on wikiloops, track-removal wise.
As for your request on "Something
more complex that could include co-existing licenses?" - I do hope the hint on the exclusiveness-aspect is answering that. There is no need to create any co-existing licenses on wikiloops end, and not on your end either, as long as you are not planning to use any remixes from other wikiloops users.
If you would like to use any tracks including other wikiloops users contributions, you may agree on a license between you and those users that covers your use-case. That'd be up to you, just keep in mind some rights have been granted and exclusivity is not to be won back.
Hope this helps & a happy weekend