let driver license expire on purpose. Good idea?

title

I'm currently abroad for job reasons and was planning to return two months after my Japanese driver's license expires. This was not planned for. For whatever reason, I thought the license expires two years after the issue date until I realized it's tied to my birthday somehow.

Technically, I could come back to Japan within the renewal period, but that would mean I need to cut my current job short, meaning I'm losing out on roughly 6.000€.

Now: How bad would the consequences be if I let the driver's license expire and try to renew it after coming back? From what Ive read, it's a deadly gaijin sin to let the driver's license expire, and I would have to beg the policeman to reissue it without taking the exam again. Driving is also really, really important to me. Good idea to just try and renew it outside the period, or should I really focus on renewing it within the time period and miss out on the money?

(Green license, never renewed, converted from a German license)

by ee_1x3