"Let's say after "Jason v Freddy" Jason is left on earth while Freddy is sent back to the burning pits of hell.
How long could Jason stay alive?
20 yrs?
50 yrs?
Perhaps forever.
Let's assume after the murders of the three hitchikers in 1999 (JGTH) the goverment totaly condemed the entire Crystal Lake community. Moving the remaining residents into new homes and paying them off in some way to 'just forget whatever happend in Crystal Lake.'
By the time Jason returned to 'Camp Crystal Lake' it was nothing more than a gigantic overgrown forest. What would Jason do, build a new shack, hunt, fish(?!?), eat, he'd live life totaly unaware of the outside world. Years become decades. Decades become lifetimes. Jason lives on.
'The Company' eventualy comes into power. The whole "Alien" thing happens. Then the events of "Aliens." Finaly at the end of "Alien 3" the lone survivor of 'the prison planet' is flown to earth. He carries a perfect alien specemen inside him. On board the space vessel the prisoner is detained and sceured, away from the crew. 'The Company' needed a totaly seculded place to conduct their alien exeprements. When Barnes found the "Crystal Lake" file it seemed perfect; abandoned for years, totaly secluded, and the 'spooky legend' would hopefuly keep any undesireables away.

The lab was designed and constructed within a 14 day time period, begining on August 8th and ending on August 22nd. The crew had one casuality to report, a class 2 licencee who was found 'hacked to pieces.' For whatever reason, Walter P. Flanagan wandered onto the work site at 22:23pm, Friday, August 13th. An autopsy conducted the following morning showed his blood/alcohol level at 0.9. His aparent intoxication coupled with the weather conditions (severe thunderstorms) were the only plausuable exeplanitions for Walters death. "Machinery Accident. Report ab/267-0800: 'whitmore tree eater: 700 series.'
The shuttle arrived 0800 hrs. August 23rd contaning one xenphobeic lifeform, and crew.
This would be a really cool movie.
Jason could kill the scientists off in his traditional manner. Meanwhile the remaining scientists would be working (unaware of jason) and eventualy the aliens would of course escape.
Jason and the aliens would battle it out. Eventualy the aliens would leave Jason for dead. Meanwhile the last remaining scientist would figure out some way to blow the lab to hell. Just as he/she is about to sacrfice his/herself for humanity the aliens break through the door and rush towards the scientist. Miliseconds before reaching their prey the aliens are stoped cold as Jason (in true jurrassic park style) bursts through the wall. Badly beaten Jason is barely able to distract the aliens as the scientist blows them all to hell.

now that would be damn cool!"