It's usually possible, though it could be a lot of work, depending on how complicated the model file is.

First thing to check is that all the models referenced are standard models (eg, bsim3v3) -- if you have a Cadence-proprietary models, then you're out of luck.

(I hope you have a recent HSpice -- Avant! was bought out years ago.)

If the library is complicated -- and you care about the complications -- then I'd recommend asking your foundry for HSpice models.  Things like corner models and statistics could be a nuisance to translate.