1. If I store Bitcoin in Trezor and eventually I lost the device
To develop your digital-asset related vocabulary: You shouldn't imagine that you store bitcoins
inside the hardware wallet. The hardware wallet only contains the
master private key which can be used to
derive the private keys of the addresses that have a balance.
So, from now on, you should say that you store your
keys in Trezor.
1. If I store Bitcoin in Trezor and eventually I lost the device, can I retrieve the Bitcoion to any other wallets, including online wallets like Mycelium, using the master seeds.
Yes, but I'd suggest on using
Electrum, instead, as it has larger community.
(And it's preferable to me)2. Can I access my Bitcoin from elsewhere using my master seeds?
Yes.
3. Since it's more like a flash drive, I guess, what happens if it got corrupted by viruses? Or any malware?
If somehow, someone malicious gained access to it, you'd obviously lose your money. Note that there are other fraudulent ways to lose money such as by a trojan. Always check the address you deposit money twice!