Unlike many other wallets, Jaxx doesn't store any user information, wallet data, or funds on any centralized server. All wallet files are stored strictly client-side, which means that Jaxx has no central point of failure. As long as you have a written copy of your wallet's 12-word backup phrase, you will be able to back up or restore all wallet assets indefinitely.
That said, while it can't be hacked on a systemic level in the same way centralized services can, Jaxx is only as "safe" as your security practices are. If you lose your device or download malware onto your computer that grants remote access, malicious users may be able to access your wallet. Sweep your computer for malware regularly, take advantage of your device's built-in security features, and use the Security PIN option, which protects all functions that can be used to remove funds or keys.