I don't know about that. The water was still a way down. If you use the water in Welly Shaft and Nangiles as a barometer, it doesn't vary that much.
Looking at Nangiles here:-

It appears that the water prior to the blow out was backed up about 6ft above No1 Level (which there is about 8ft above Jane's adit level). If you look down the engine shaft now, water at rest is about 6ft down. It probably drops another 2ft maximum. I have never seen any water levels in any of the shafts rise much above what they were. I've seen the adit level in welly very wet due to water accumulation, but never the water in the shaft rise.
If they did have a catastrophic pump failure, the Jane adit is very secure. All the shafts on it and all the stopes connected are effectively a resevoir. They've got about 8ft or so of elbow room before Nangiles level starts to flood. This itself amounts to a huge run of stoping. The Coffin levels in West Jane would effectively become huge lakes, there is another run of massive flat stoping through Wheal Widden, when the water rises to the Nangiles adit level, you have that massive tunnel which can fill, and then all the workings on the copper lode, as well as a pretty damn extensive adit system. When you consider the welly side, Wheal Andrew as well as all the stoping (very extensive above adit on the old old plans) it runs into probably 6 figures of cubic meters of space!
It would take a fair old time to fill up. You'd have percolation right over to Ting Tang.
At the moment, with things being adit level, or there abouts New Jane side, they've got about 8ft of headroom before they get to the point immediately after the blowout happened. Things were allowed to fill up about another 6ft above that (looking at the levels on the walls in Nangiles). So, they are 12ft below the point at which it was backed up to.
So, we have to ask ourselves the question, did they sort the blockage in Nangiles which blew out after, meaning they have 12ft of headroom? (Probably not).
If they were to switch the pumps off, I imagine the water would rise in Old Jane and New Jane flooding the deep adit system completely (and ruining several precious habitats) big lakes would form in the West Jane Stoping and the water would rise in Nangiles, completely flooding the copper workings beyond Tregonning's shaft.
Then the water would rise to the adit level in Nangiles (which is approx the same as that in wellington according to the section) and flood to the point that the breach happened last time, or one of the blockages would eventually give way.
When you consider the sheer amount of water in there (+6ft in the whole run of mines) it is a mind boggling amount.
I'm not sure that the adit politics at Jane will be resolved, so a sensible person would suggest that the water was allowed to exit via a refurbished system at Welly.
I wonder how they arrived at the 12 hour figure and I wonder how well the people who are in charge of this water business understand the situation. Of course, they will be experts, the consulting geologist will have probably doctoral experience in modelling mine-water rebounds and prior to the disaster, they will still have the data which can inform the likely progression of rebound with the rainfall. They will have confidence intervals, operating parameters and backup insurance measures.
It would be hugely cynical to say there was some hillbilly called Dave who says "fukin ell, the waters come right up, get someone with a bloody fire engine!!"
It might be an idea that this ambles a bit further towards the "what are we going to do afterwards" stage of thinking....which, behind the scenes, they are doing.