From my understanding, if the crowdfunding is successful, all of the gathered ether is sent into the ICO wallet, meaning the contract is left without any ether. Doesn't that mean the token becomes worthless, since people can't exchange it back to ether since the contract can't give any ether.
People will expect that someone else will buy their tokens. The idea is that the token value will go up because the team will use the money you have given to build something of value, therefore, people who want to use the services will need to purchase the tokens (hopefully at a higher price). The main idea is that you are taking a risk by investing in an idea. If the idea is successful you will be rewarded for your vision.
All that said, what you imply is what I would like to see. A ready to use service based on a token that is fully backed up.
As I have conducted an ICO, the token value is increased based on demand and supply. If your idea behind the ICO is solid, then people will chase for your token and gradually the price of your token gets lifted.the value of the token will get depleted,if none of your token holders use it.So create a reason in your ICO,so that people will get attracted to your token.If it helps you,please upvote.