Thanks a lot! We're already experimenting and trying to see where can we take this concept further. We have in fact experimented a little bit with ways for the reroll meter to recharge and have already considered both options you mentioned (we're currently tweaking things and trying ideas out). It is indeed true that if you run out of any rerolls the combat starts to fall flat, so we are in fact working on getting something that both makes the player feel like they have control while still maintaining the challenge and the uniqueness of the game's primary mechanic. And I am glad to say we made great progress on that. Hopefully in the future we will be able to release a post-jam version with all the ideas that didn't make the cut to the jam, and everything that did tweaked and polished even more!

Thank you so much! We have in fact started working on a post-jam version already, where we properly explore all the mechanics we wanted to in depth, primarily the dice customization feature. So thanks for the kind words! And expect a post-jam version pretty soon! :D

Thank you so much! We do plan to continue the project, and were on the verge of having five levels instead of one when the deadline got close. We plan on releasing a more polished version after the jam with all the ideas we had initially. 
In terms of making the mechanics more complex, the initial plan was to allow the player to customize their dice, and the encounters were meant to support different dice builds. For example for one fight you might need a more offensive build, and for the other you might need to give your dice more "Defend" faces.
In terms of uploading to mobile, if it's possible to do so with Godot and we continue the game to a point we are proud enough in we could potentially attempt to upload it to mobile. 

TL;DR: Thanks a lot for the kind response! We are in fact continuing the game and making the gameplay more in depth and more balanced :D

We already have a plethora of ideas for the game, which we are currently working on just for fun and might release at some point in the future. The elemental multiplier idea sounds really cool, we might consider adding it later down the line.

Thanks for the feedback! We have in fact managed to add much less then we hoped to the game jam build. We initially planned on having around 10 battles ranging in difficulty and enemies, as well as an option for the player to customize their dice before each fight (and therefore adding more depth to the strategy of each fight). The enemies were also intended to support this, with each type having it's own unique dice and probabilities (though we only managed to finish slimes on time). We do plan to update the game after the jam, making it more of a game and less of a design idea (like you said it currently is), so if that might interest you stay tuned!