Maybe a small amount of miners take their profits and then re-invest back into their operation, but if the money keeps on rolling in, I think they're happy with what they're mining.
So no miner has any savings in bitcoin that they HODL in your opinion? That sounds really unreal.
I can understand using BTC as money, but generally speaking bitcoin is technically a commodity, plus people already do save in money, especially bitcoin users who try to avoid fiat.
So with those assumptions I guess any miner has at least 10-15% of his profits saved.
I think that a year or two ago, before the halving was so close to occurring, there would be a lot more miners who would just take the straight exchange and then go do whatever with their funds. Now that we're bordering on the halving, I have a feeling miners are holding more than 10-15% of their profits and are waiting for the halving to roll around. I think some miners are holding upwards of 40% of their funds waiting for the halving, but I'm not a giant Chinese Bitcoin mine owner, so I am not entirely sure.