If TMNT:BTTS did end after this season, I would not be in favor of another TMNT cartoon beginning any time in the near future. The 2003 TMNT cartoon started less than 10 years after the original TMNT cartoon ended. And that was ok because the world was ready for a TMNT cartoon that did justice to the characters. The TMNT franchise was in need of a darker version that more closely followed it's comic origins. Another TMNT cartoon created immediately after this one ends would be created for one reason, and one reason only, profit.
Also, I really wouldn't be all that bothered by this show coming to an end after this season. Seasons 5,6,and 7 have all been steps down from each previous season. The show felt like it was at it's absolute best during seasons 3 and 4. Season 5 was just about a 1/2 step down from those seasons. Season 6 (the Fast Forward season) was a major step down. And season 7 (the BTTS season) feels like an even further step down. So while I felt like the end of season 5 would've been the perfect place for the show to end. I'd be ok with this show being put out of its misery after this season.
Also, I really wouldn't be all that bothered by this show coming to an end after this season. Seasons 5,6,and 7 have all been steps down from each previous season. The show felt like it was at it's absolute best during seasons 3 and 4. Season 5 was just about a 1/2 step down from those seasons. Season 6 (the Fast Forward season) was a major step down. And season 7 (the BTTS season) feels like an even further step down. So while I felt like the end of season 5 would've been the perfect place for the show to end. I'd be ok with this show being put out of its misery after this season.