Just rooting around on rsssf.com as you do, and I found Velbazhd Kyustendil again! After they "merged" with Lokomotiv Plovdid the year after we played them, they reformed in the Southwest regional leagues (third flight), and have been there ever since. 2002/03 is as recent a table as I can find on the website - they finished 12th out of 18.
Checked their 2000/01 campaign - lists full goalscorers and everything. The names come flooding back! (If like me you have the highlights of the match on video...!) Mihail Mihailov was the league's second top scorer with 17 the previous season, but doesn't feature at all in 2000/01, so he must have been sold abroad or gotten seriously injured...