If they had stayed it would still be going on today. Again what is your definition of lost? You seemed to confuse what a lost really is. If lost means white flag, signed treaty of surrender than no.
It would be impossible for the US to lose. At worst they deemed the war not worth it anymore, pack up and go home like they did.
As I mentioned to even compare Vietnam to the current Israel/Palestinian is ridiculous as the dynamics are totally different.
Both sides believe they are each fighting for thier own very survival be it real or projected.
Vietnam wad never about survival. It was more about ideology and a proxy war with the Soviets.
I don't think so.
What would the situation be like if the US Army were still in Vietnam today?
What we should have seen is US conscripts refusing to join the US Army for decades, knowing they they be sent to Vietnam. Professional soldiers world also be burnt out from knowing they were in a pointless and immoral war where they were the bad guys, and would leave.
So there would be a much shrunken US Army presence. Arguably this would be small enough that the Vietcong could start defeating.
At the same time, the cost to the US would keep increasing upwards to literally unaffordable levels.
---
Over 3.1 million soldiers were sent to Vietnam over a roughly 10 year period.
So if the US were to have maintained this level to today, that implies another 15.5 million soldiers would have been needed over the past 5 decades. I severely doubt the US Army could find or coerce enough recruits.
In the real-life timeline, the US Army was already broken by Vietnam. Yet you say the US could sustain another 5 Vietnams?
---
In terms of cost, the estimate was roughly equivalent to $1 Trillion today, mostly spent in a roughly 10 year period.
So if the Vietnam war was still on today, that's an additional $5 Trillion added to the US national debt.
If the original spending timeline remains, that $5 Trillion would compound to ridiculously high levels to an additional 100%+ of today's US GDP.
Of course, this wouldn't have happened, so there would been tax increases or domestic spending cuts in the USA.
---
Arguably the US economy had already been broken by the real-life Vietnam war.
Yet continuing the Vietnam war for another 50 years is feasible?