More formal way to say "just in case"
Solution 1:
The "just in case" part of your question is written from your perspective. You want them to contact you "just in case". There is no need to risk confusing the person to whom you are communicating by addressing issues from your viewpoint. Instead, write in the language and world-view of the people to whom you are communicating.
Please have xyz contact me next week, to address any unresolved issues I may have.
Solution 2:
It's a fine distinction, but I think a slightly more "formal" phrasing would be...
Should anything remain unresolved, I'd like someone to follow up.
...but if you want to sound really formal/starchy, consider...
Lest any problems remain...
Solution 3:
I'd like XYZ to call me next week in the event that there are unresolved issues...
Solution 4:
Why not call it what it really is?
Precaution
An action taken in advance to protect against possible danger, failure, or injury; a safeguard: followed safety precautions when using heavy machinery.
Caution practiced in advance; forethought or circumspection: a need for precaution when planning a vacation.
With this in mind, you may say something like this
As a precaution in case something happens, I'd like someone with Volkswagen Corporate to follow up with me next week.