Norway runs almost entirely on hydropower. Sweden has a lot.
Iceland runs on hydropower and geothermal.
Very simplified:
Wind blows mostly in Denmark during the day, so Norway stops hydro during the day and imports electricity from Denmark's windmills.
During night the wind is mostly still in Denmark so windmills don't produce much and Denmark imports from Norway's hydro.
In this way you can stretch the capacity from hydro using windmills even though Norway isn't a good place for windmills.
So it's not going to take off like solar but it's a big chunk of relatively clean electricity production and it's often basically a byproduct of managing water supplies. It also pairs really well with renewables as even without pumps it has a degree of flex and storage.
In the US capacity is likely to go down (dams are expensive and many time old dams are removed instead of being rebuilt).
I mean it is, its just slower.
but if you have batteries, then you can divert the power to the batteries to keep them topped up.
If you're using it to charge batteries it's just five times more expensive than equivalent solar or wind.
The point is, with enough battery, you don't need fast despatch for things like water/gas/nuclear, because the battery does that for you. In the UK the 11gwhr we have (about 1/2-1/3 of one hours consumption) is more than capable to do the balancing.