A vasectomy is a permanent surgery and should be viewed as such before you decide to go ahead with the operation.
Although it is possible to have a vasectomy reversed, the procedure is not always successful. There is a better chance of a successful reversal if the surgery is done very soon after the vasectomy. But it is worth mentioning that this reversal procedure is far more complicated than vasectomy itself.
If a reversal is carried out within 10 years of your vasectomy, the success rate is about 90%. This success rate drops if your reversal is carried out more than 10 years after your vasectomy. As demonstrated above, success rates are not perfect and there is no guarantee the procedure will work. Moreover, pregnancy still may not happen after a vasectomy reversal because your sperm may be less mobile than they were before.
So even if a surgeon manages to join up the vas deferens tubes again, pregnancy may still not be possible. This is why you should be absolutely certain before going ahead with the vasectomy.