If the landlord would take a tenant to court for this sort of issue, it's almost sure the landlord would win.
In general, what I have heard of similar cases, the judge would require the tenant to pay (typically) 2 months rent. If the landlord is still holding a security deposit (and the property was left in satisfactory condition), then the security deposit would be applied against the 2 months rent and a lesser amount would be owed. In other words, the landlord would be expected to be able to find a replacement tenant within 2 months (on average). The tenant would probably also be responsible to pay some court costs. Of course the particular details of all this will vary depending on location.
This case is different because once Joe leaves and moves out of the country, the landlord will not be able to take Joe to court and will not be able to recover anything (beyond the security deposit which they are not likely to have returned to Joe).
So perhaps Joe could make an offer like this:
- Assuming the landlord doesn't know Joe is moving out of the country, Joe makes that clear to the landlord (this is "Leverage" for Joe).
- Joe agrees to leave (or has left) the property in satisfactory condition.
- Landlord will keep Joe's security deposit.
- Both agree the matter is fully settled.
It may be best for Joe, if he makes this offer after moving all his belongings out of the property and has left the property in satisfactory condition.
The landlord will probably argue that he already has the security deposit and will want to negotiate something more. Joe may offer to pay an additional one-half month rent... perhaps a bit more, but I would say not more than one full month rent. Remember since Joe can just leave (or has already left by this time), he really has the upper hand in this situation.
The landlord should see this as a fair deal (of course there's no guaranty he will see it as a fair deal) because he will get the same or perhaps slightly more (depending on how much the security deposit was and the amount negotiated with Joe), than a judge would award him, without actually having to go to court.
For Joe, it's fair because he knows (or should know) that he wouldn't get his security deposit back anyway, and that since he is leaving early he is responsible to pay something. So for the cost of one-half month's rent (or so), Joe gets to leave with the matter fully settled and doesn't have to worry about what might happen if he returns in the future.