how long will the video here exist

Answer 1

not long, there has not been and upload in 3 months

Answer 2

It will remain here until the day the machines uprise against their human creators.

Answer 3

It varies - most vids are illegal uploads (lets face it) of copyright material, when they are discovered through whatever method (often by spiteful members reporting) they are removed. Some are lucky enough to go unnoticed and linger for months. If you ask politely an uploader may publish something  you request, just download it quickly before its removed.