So getting ganked by a jungler with red buff is almost a 100% dead end if there is no flash or mobi?

depends on the jungle champ. Depends on your champ. Depends on how overextended you are. Depends on your enemy lane champ/champs.

A lot of factors, there is no definitive yes or no to your question.

As a jungler. Yeah pretty much as long as you overextended enough

Not even a little bit. Basically don't be bad and actually ward, or learn to buffer abilities lol.

It's called "map awareness".

Get some.

Your simplifying a complex issue - there is SO much that goes into it. To even begin to have a shot at honestly answering your question you need to answer all of the following

1. How overextended are you?
2. How close are you to your lane partner?
3. How far is the enemy Duo from you?
4. What champion are you playing?
5. What champion is your lane partner?
6. What level are you?
7. How skilled are you at Juking skillshots?
8. Do you have any crowd control or slow abilities?
9. Do you have any abilities that speed you or your ally up?
10. What is your health at?
11. What health is the jungler at?

Go ahead - set up a scenario.

I was playing Yorick last night, and was dominating my opponent toplane (Jayce). Around mid game I was pushed right up to his tower and his Rammus jungler attempted to gank me.

I was so far ahead I fought both of them at the same time, killed the Jayce and then just simply walked away from Rammus because of my W and E.

So, to answer your question, it depends.