1) How does it make sense that it is based on who survives the longest ?
You shouldn't see it as a part of Warlight or Warlight FFA, you should see it as something that is a property. Sure, it can be gamed, but that becomes part of the game. As you suggested you can "bait" the other players to gang up (which another team may or may not believe - and even if you do believe them ganging up on this opponent may open up a win for a team that doesn't really care as much about taking that team down), you'll generally spend more resources on finishing teams off, because it will mean assurance of extra points, you could try and keep a weak team alive as there is another team that is ranking well you want to kill first, if your rank is good, you'll have to do better because people will be more aggressive towards you.
2) If people get a higher rank from a tie, who is to prevent them from both voting to end to garner the much needed 10 points for both of them. I mean apart from voting to end...what other means would merit a tie, I don't see them.
I agree. I would suggest (1) defining a tie as being killed in the same turn (you could look to move order, but that makes little sense to me), (2) having teams below the tied teams not get extra points (i.e. when team alpha destroys teams beta and gamma in the same turn, while team delta was already out of the game, teams beta and gamma get 7 points, while delta only gets 1` point. Basically, it makes little sense to reward gamma for beta and gamma having tied - the only time I have seen it done as you described was when the organizers had accidentally twice the amount of medals then would normally be needed) and finally (3) when the game is ended through voting, the remaining teams get the points the team to be taken out of the game would (i.e. When no team has been defeated at this point, all teams get 1 point - if nothing else this should prevent strategical voting to end).