InfoPath Dev

I have lots of forms published to sharepoint all with a workflow to send emails etc. but after someone submits a form it could be weeks or even months before the form needs to be opened and progressed - does the workflows expire at all or will they always work and send the emails even after weeks of just sitting in the sharepoint library?

Thanks.

Not exactly, but if an admin "removes" the corresponding version of the workflow associated with the item, it might cause the "thread" to "disappear", even though the item/document will remain.

If you have a more recent version of same workflow, it will not "take over" the action of the old one. It will activate on a document change though, if set so.