You can use your Monero wallet seed with most other Monero software. Should SendMonero.to be unavailable, your money still belongs to you and you can manage it using other wallets.
Monero allows you to manage your own money without proving your identity or justifying your existence. Sometimes you will need to send money to people outside of Monero. To pay a friend, a utility bill, or buy a house. SendMonero.to makes the connection between your private cryptocurrency and the legacy banking system.