Does proton decay produce quarks and other elementary particles and what is the time frame involved ?

Within the standard model there is no mechanism for proton decay. Hypothetically, the proton could decay into any lighter particles; provided we break some of the symmetries of the standard model, in particular baryon number. Experimental bounds on the lifetime of a proton is of the order 10^33 years.

Quarks don't exist alone, so would they be expected as a decay product?

Quarks don't exist alone, so would they be expected as a decay product?

They would not be expected as free particles; one commonly explored decay in this context is into a positron and a neutral pion.

There are actually a few theories that predict proton decay via the Higgs Boson. The proton would have a half life of about 10^36 years though.

The proton decay was fashionable at a time when the proton was considered a fundamental particle. Now as a complex building of more particles, it would involve many reactions simultaneously to decay into, say, two elementary particles. So is the decay still so fashionable?

So is the decay still so fashionable?

Such a decay would signal some physics not accounted for in the standard model. I guess there will be some interest in proton decay for a while.