Important question about Light and L after Ep 25 Silence (Spoilers)

First of all, I love this series. I rate it a solid 9.9/10.

The series dies to me in my opinion, after episode 25 however, for obvious reasons (Near and Mello are nowhere near L, Light kind of gets lazy with Kira, etc...).

I do have one important question.

L dies planning to try the Death Note for real with a prisoner who was senteced to be executed in 13 days, to foolproof the 13-day rule that "cleared" Light and Misa from being Kira. Let's keep in mind L dies of a heart attack.

Now here are my thoughts:

1. Since L dies of a heart attack, shouldn't the investigation squad assume that L was killed by Kira, either directly or indirectly (even if Rem died)?

2. Having that said, why didn't the task-force go on with L's plan to try the notebook for real? With L dead (murdered by Kira), it adds more weight to foolproof the 13-day rule, or at the least, to find out whether if L's theory was right?

3. After L dies, Light is obviously not the direct responsible of his death. However, if Misa is free and having all the evidence against her pointing that she had to be Kira at one point, the only thing saving her is the 13-day rule. Shouldn't the team-squad have Misa arrested again?

This is why to me, the series ends after episode 25. In fact, I watched episodes 26 and 27 hoping that was what was going to happen, but since it didn't, I just quit watching it altogether.

To me Death Note is a 9.9 out of 10 from Ep 1 to 25. From Ep 26 and on, it has a HUGE plot hole to answer to.