Being offline does not ensure security against unverified plaintext. Imagine a colossal implementation fuckup (e.g., using strncmp to verify tags, ala Nintendo), or perhaps a hardware glitch flipping the verification bit to always return true. Ideally, i.e. with a robust AE scheme, you would hope that an altered ciphertext would result in random plaintext, but in SIV this is not the case.
Alas, there are no standardized robust schemes, with AEZ making it to the CAESAR final portfolio being the most likely scenario of that happening.
AEZ uses a non-standard AES variant in a sui generis fashion; as a result some people have called its security into question: https://eprint.iacr.org/2016/832.pdf
Point being, its inclusion in the final CAESAR portfolio is far from clear at this point.
Alas, there are no standardized robust schemes, with AEZ making it to the CAESAR final portfolio being the most likely scenario of that happening.