Had a port a cath removed due to a blood clot in the superior vena cava. should this clot dissolve on its own ?

Maybe: Blood clots in a major vein are often treated with anticoagulant medication. While it may dissolve on its own after port a cath removal, medical treatment is commonly recommended. Each person's conditions are different, however, and would need input from your doctor.

In a manner : Hopefully flow through the svc will be restored, but may never be normal again. The threat of embolization is minimal. Hopefully there are not other factors causing the clot.