Any option other than an implant?

My molar was treated for root canal in 2006.  18 months after that, I started noticing a "bubble" on the gum above the tooth, as well as some minor pain and numbness in the area.  The bubble would come and go.

I went back to my Endodontist for a re-examination, and she said there's nothing wrong with the root canal, and suggested that I go see a Periodontist.  The periodontist noticed some bone loss, and did an Osteoplasty on the tooth to fill in some bone.  A year after the Osteoplasy, I noticed a bubble + pain + numbness again, went back to the Periodontist, he said it might just be some food particle getting into my gum pocket, and suggested that I do a few sessions of root planning.  Did that.  

Six months later (last week), I went to another Periodontist to get a second opinion.  He said that the pocket on the gum is deep, and the x-ray shows that there's still bone loss.  He recommended me to go back to my endodontist to re-evaluate the site again, if there's nothing wrong with the root canal then there's got to be a crack in the tooth, it cannot be anything else.

I have three questions:
1) If my endodontist still sees nothing wrong with the root canal, is there anything I should do before having my molar removed (and have an implant)?
2) The (second) periodontist says I should have my gum open to check for cracks first before removing the tooth, but even if none is seen, there's got to be one.  So is there any point to open my gum to check then?
3) If my molar is indeed cracked, is there an urgency to remove it?  The pain isn't that bad for now.

Thanks!