If the miners decide to switch to another altcoin you cannot sell any of your coins - no matter which coin it is, even Bitcoin. If they reduce their efforts prices to transfer becomes extremely high. If you have a lot of your money in cryptocurrencies, the miners will become your new slave masters
I don't agree with this. Ultimately the final say is up to the market support. Miners are running a business, so they will stay were the profit is. The market is build on supply and demand, so if we demand bitcoin for example, like is happening right now, miners will stay in bitcoin because it's more expensive, so it gives them more profit. Yes, they might switch to some other coins from time to time (like bcash), but they will only stay there if we start selling our bitcoins and start supporting bcash.
If we don't swap our coins, they will just have to come back. If they don't, then difficulty will adjust to the new hash power, and we will still be fine. If difficulty decreases, then it will be even more profitable to mine BTC, so again, in the end, miner will be where the profit is, and the profit is where the demand is, so we are not slaves.
The miners can drive up transaction costs for you without you being able to do anything about it. The Chinese mining farms are becoming so big that you cannot hope to compete yourself.