Many but not all. Sia for instance will continue to exist independent of the company, it is fully decentralised. I believe your statement is true of StorJ as they rely on centralised services but I can't comment on the others.
Bitcoin would continue to exist without the exchanges and wallets, they are peripheral to the core technology. Blockchains can't be 'forked at a whim' without majority consensus, that's the whole point. ETH is the obvious example where the devs forked with support from the community and it led to the ETH/ETC divide.
What you would do if developers turn corrupt and force a new version with unwelcome changes? Most people see developers as some kind of robots, but cryprocurrencies are often fraud schemes where developers control the market.
Well consensus can be manufactured or ignore smaller players. e.g bitcoin seqwit hard fork was decided by large-scale mining companies.
If a small cryptocoin you have most of the hashing power in some side company, you can fake it as majority of miners consensus.
Bitcoin would continue to exist without the exchanges and wallets, they are peripheral to the core technology. Blockchains can't be 'forked at a whim' without majority consensus, that's the whole point. ETH is the obvious example where the devs forked with support from the community and it led to the ETH/ETC divide.