Does lasik surgery to get 20/20 vision again last forever?

Not always. Lasik generally gives excellent results rapidly. A few do not hit the target and can be enhanced if the last improvement is important. Over time some 'regress' which means the eyes lose some of the improvment. This can also be fixed. When you get over age 40, with a perfect result, you will start of have near vision issues (presbyopia) which happens to everybody.
Ideally . Although it is very rare, a follow-up lasik procedure may be necessary if your eyes do not heal as expected. Lasik is permanent, but not a lifelong cure.
Yes. Lasik corrects your vision and there are good studies showing long term stability up to at least 15 years. Unless you develop other eye issues such as cataract, glaucoma, macular degeneration, or others, your vision should be corrected from now on.
Not really. Our eyes change with age. This means lasik will not last for ever. After lasik surgery the patient may remain stable for many years or it may regress. Person after 40 will become presbyopic(loss of near sight) then he/she may need reading glasses. After 50 or later cataract development will change our refractive correction or need.