There are really 3 options here.
1) Wait out the water. The figure being quoted is 4 months until the end of the rainy season. 4 months in a cave is a loooooong time. And it's going to keep raining, which means their dry spot might not be so dry for long. It also raises other issues that make it less than ideal.
2) Drill a bore shaft like a mine rescue. This is probably the "safest" option, but it's also the most logistically intensive. Getting a drill up into the mountains is not going to be easy. They weigh like, 30 tons, and depending on the type, require a staged boring operation. The terrain sucks, locating them topside sucks, overall the whole thing sucks. It would also take a decent amount of time to actually get the hole to where the kids are. The Chilean mine rescue took a month of drilling, and that's after they knew where they were and already had bore holes through which they were able to resupply the miners. That was to 700m.
3) Teach the kids to swim out. You don't have to teach the kids to be cave divers. You need to teach the kids to equalize and remain calm, follow a line, and move slow and easy, purge a FFM [full face mask], purge a mask, swap regulators. Really they don't even need to know how to swim. It's not a massive push dive, it's sump diving, of which there's at least one no-mount restriction. That is the difficult part because you cannot control the kids once you get to the restriction. However, put them in a full face mask with comms so the Thai divers can talk them through it, and you maximize their chances of getting out alive. No-mount restrictions are no joke, but they're not impassable. We do it all the time in cave diving, and while I'm never super comfortable with them, I'm also not peeing myself at the thought. Given the right kind of support, training, and psychological preparation, the kids will be able to do it. Remember, most of these kids are half the size of the divers that made the push. That all helps. Hell, you'll probably turn a couple of them into future cave divers.
They appear to be going with option 3 as they've already started teaching the kids how to dive. They're already improving the cave to hedge their bets against anything untowrd happening, running lines that can be used to pull as opposed to simple cave line, staging tanks along the whole route through the sumps, adding auxiliary lighting, etc. They're doing everything they can to maximize their chances of success, and the Brits are the best in the world at this type of rescue. If it's gonna happen, they're the ones that are calling the shots on how it goes down.
My opinion is based on 1) being a cave diver, diving in squirrely places where you have to take your stuff off to fit, miles from air, 2) having family in mining who know a hell of a lot about that side of things, and 3) being familiar with those CDG guys, their qualifications, and their track record of doing stuff like this. You want to pull someone out of a deep cave, call the Finns, you want to pull someone out of a sumpy mud hole, call the CDG. This is a sumpy mud hole and they've got the best guys in the world leading the way.