That would depend on what you mean by 'off Atkins'.

If you resume the old eating habits that caused you to gain weight in the first place, then yes, of course it will cause you to gain your weight back, and likely plus more.

If you mean that you want to try another way of eating for weight loss, then it would depend upon your body. You might initially gain a few pounds going back to eating more carbs. Those pounds would likely be from fluid retention, not fat. CarboHYDRATES Get that ....HYDRATE? Right in the name it tells you that a carb is going to cause water retention! When your body adjusts to living with a higher carb count, you should drop some of that weight again, but you won't drop it all. So long as you are eating more carbs, you WILL be retaining more water than on a low carb diet. The carbs just do that to you.

But you shouldn't regain all weight lost, if you watch your limitations of your diet.... like watching calories.
UNLESS..... your body prefers the low carb, high fat way of eating. Personally, for me, clearly my body does better eating this way. I need less sleep, have oodles of energy, never have a headache, never feel bloated and miserable. But thats just me. You might be different, and I am not going to preach to you. There is no one diet right for everyone, no matter what people here might say. Listen to your body and follow its lead.

You might look into the South Beach diet. I have friends who have had great success following that lifestyle. I believe it uses more carbs initially than Atkins.