What appears or does not appear on a credit report is meaningless. With medical debt, it is who you owe when it comes to getting a Visa. If a public hospital, you may be excluded from returning without a sponsor's affidavit of support. Hope this perspective helps!
As to the debt collection question, the time you were away would toll the statute of limitations, should a creditor start collections; however first they have to find you, which may be a cold trail, unless you help them with collections information.
As to the effect on immigration status, that question may be better answered by posting the question in that category.
General legal advice is offered for educational purposes only. A consultation with a qualified attorney is required to determine specific legal advice as to your situation and applicable law. We are a debt relief agency and we help people file for relief under the bankruptcy laws.