No point in giving him a fifth year when Miami and Houston doesn't have the cap space to match 4/44. They're bidding against themselves if they surrender a fifth year.
How is Isaiah's defense? I haven't watched him much. And Avery Bradley is not a point guard.
I think if Lowry leaves, the best replacement available would be Darren Collison.
I've heard quite a few people say they shouldn't overpay for him and instead trade for Rondo and extend him to the max.
Lowry > Rondo all day everyday.