What happens if i ignore shoulder tendonitis?

Frozen shoulder: You may end up with a frozen shoulder (adhesive capsulitis) and essentially will not be able to move your shoulder.

Depends: Tendinitis is not always symptomatic. If it does cause soreness, make sure you at least maintain your range of motion. Otherwise you can live with tendinitis without much fear of causing additional problems. Tendinosis is slightly different in that there can be deterioration and eventual tearing of the rotator cuff.