I feel like this is really simple to fix.
Just show Han's death scene from another angle, where he crawls out of the window while Shaw is walking away and escapes into a manhole. So in Fast 9 he shows up with a rival crew along with Lucas Black.
Dueling families. Sounds awesome to me.
Also, I assumed that Eastwood's character was there to fill the gap that Lucas Black left when he unfortunately dropped out. Damn TV filming schedule. Could you imagine if after Tokyo Drift Black got a job with Nobody?