If you leave your 401 (k) with your previous employer, you will no longer be allowed to make contributions to the plan. With a 401 (k) counterpart, you can only keep the amount you contributed if the money was deposited in full before you quit smoking. Otherwise, the former employer will eventually recover all unearned contributions. Fortunately, the money you have contributed will still belong to you no matter what.
You can contribute up to a certain amount each year, and it's possible to contribute to both a 401 (k) account and an IRA in one year. From a tax benefit standpoint, the IRA works in a similar way to a 401 (k), minus your employer's contribution, of course. What you should keep in mind in this situation is that you will no longer be able to contribute to the account if you stop smoking.