The http://www.uesp.net/wiki/Oblivion:Mages_Guild_Suspension is pretty helpful in general, and here, too:
Second Offense
After your second offense the procedure is nearly identical to the first offense. You are again sent to collect 20 Dragon's Tongues and 20 Redwort Flowers if you committed theft, or 20 Daedra Hearts and 20 Vampire Dusts for murder. The only difference is that this time around you must have 20 of both requested ingredients.
[http://www.uesp.net/w/index.php?title=Oblivion:Mages_Guild_Suspension&action=edit§ion=6] Third Offense
After your third offense, you are permanently expelled from the Mages Guild. The most serious implications are that you will no longer be able to access the Enchanting and Spellmaking altars and be permanently denied the services of http://www.uesp.net/wiki/Oblivion:Boderi_Farano (Advanced http://www.uesp.net/wiki/Oblivion:Mysticism Trainer), http://www.uesp.net/wiki/Oblivion:Martina_Floria (Master http://www.uesp.net/wiki/Oblivion:Illusion Trainer), http://www.uesp.net/wiki/Oblivion:Gaspar_Stegine and http://www.uesp.net/wiki/Oblivion:Borissean (Spell Merchants): they are all residents of the Arcane University, which will be forever closed from you.
If you are Arch-Mage it is impossible to get permanently expelled; you just receive a normal bounty for any offenses that you commit.
The theft thing seems reasonable enough. I would rather see all the fruit and veggies made just as restrictive as the meat, and all of it made more restrictive than it is--and there's a mod I use for that. But it's understandable that many folks wouldn't see things that way. Best of luck, regardless.