Your Solidity contracts can run on Ethereum Classic, which you can be confident won't be forked since its users tend to believe in the principle of the immutability of the code.
The classic branch is still susceptible to the same problem, though. They didn't fork because of the DAO, but who's to say they won't fork because they don't like the result of a different contract?
If I'm going to trust the enforceability of my contract to some group of people, I trust the established legal system--warts and all--much more than the mob rule of the Ethereum crowd.
The dev team for Classic is much less likely to attempt to do so, and the miners less likely to adopt such a fork, since they declined to accept the fork the first time it happened.
If a fork happened in Classic to protect some party's financial interests, I think the more likely scenario is the great majority of miners opting to stay on the original branch.
I get that it's not a complete guarantee, but neither is the legal system. Contracts can be invalidated based on a judge's perception of their unfairness, on a technicality, or even on a whim.
I'm not wholly on one side of the fence or the other on the fork. But since the decisions made by the community involved can affect your holdings, it's reasonable to advise people to choose the community that has similar values to them.
Unless they're interested for purely speculative purposes, in which case it was a good bet that the non-Classic version would be more remunerative.
If I'm going to trust the enforceability of my contract to some group of people, I trust the established legal system--warts and all--much more than the mob rule of the Ethereum crowd.