He will probably either die become a slave or exile. He was never in the running to inherit the kingdom because they already crowned their prince. So really he's just a sore loser. At best he would have been a duke. Probably married off to a Duchess of another country.
more that the tone of the series is rather light, all things considered, due to the inherent comedy of an outrageously overpowered MC.
The soldiers hit by the gigantic marble pillar weren't flattened into bloodsmears inside crumpled armor or smashed against the wall leaving craters and broken bodies - which I take to mean that the seriousness of the setting isn't particularly high.
So he might get exiled, but the series up to this point doesn't quite have the feel of bestowing realistic levels of consequences that would otherwise line up with what the prince has done.
Though I could see him simply being "executed off-screen" and it's just mentioned as a throwaway line - but death does not strike me as a real result of actions taken by characters here (outside of the MC necessarily dying in order to reincarnate, I suppose).
And that's fine, it doesn't have to go that more serious route, as this is very much a silly, slapstick manga thus far. But sometimes it gets a bit difficult to suspend disbelief when very dumb decisions made by characters don't result in equivalently severe repercussions.