Did L's plan not depend on the event he did not anticipate? [Spoilers]
Consider the scenario from L's point of view (where Rem does not kill Watari and supposedly L, since L cannot make any assumptions about sympathetic reapers).
They would have arrested Misa as she tried to write his name down. She would have then refused to give up Light and died in the process. Meanwhile Light continues to play it cool and eventually L ends up dying. As he says in his monologue at the end, the only thing he needed was for Light to drop his poker face; this was only accomplished due to him faking his death, which he improvised when Watari died unexpectedly. Granted this leaves Light with no DeathNote and the movie would have no conclusion but I'm just saying that L either made one hell of a gamble, or this is a plot hole...
Also, I'm a bit fuzzy on the details since I never read the manga, but the movie seemed to imply that you could only use the DeathNote once you had taken ownership (which in turn only occurred after you killed the current owner - as demonstrated by Light killing the reporter). Does this not mean that L needed to kill Misa to take ownership? Or is this only relevant to the bit about memories? Does this mean anyone can use the DeathNote even when it does not belong to them? In which case what is the point of taking ownership? If you can have all of the perks of DeathNote with none of the disadvantageous (i.e. limbo, memories, distracting reaper), surely this is the preferable option for a genius like Light?
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The two of you killed everything I ever loved. **** you both.share