A review of the Trezor hardware wallet says:

In order to access your coins, you would simply do so by connecting your TREZOR to your computer and power up the TREZOR wallet interface at https://wallet.trezor.io. From here, you can see your balances, generate addresses for payment, and send payments.

If trezor.io disappears for any reason, is the Trezor hardware device useless? Are there other ways to spend cryptocoins tied to the private key in the Trezor that don't depend on trezor.io?