Although what's done is done in OP's case, buying tickets in fare buckets where there is no residual value of any kind if not used excatly as booked, is always extremely risky.
OP's situation happens to surround a visa issue, but this could just as easily be any other messy situation.
The real key is to always double-check the fare rules for the specific ticket which you propose to purchase. First, the rules may have changed since the last time you bought one. Second, the reason that fare codes are 5 alphanumeric characters is that there are variations even with broader categories.
DL is piloting deeper than usual discounts in return for zero flexibility. There is a market for these tickets, but they carry real risk. Some risks can be insured (health, job), others are less likely (legal problem such as OP's).
But, unless you can afford to lose the entire value of an international ticket, it's critical that people you spend the time to at least read the key provisions dealing with refunds & changes.