Not at all, you can only be given benefit of your previous service but they are not liable to take you back, so better is to apply again if any vacancy in future arises. 

You need to apply the same and see to it that your application is entertained as per service rules. It also depends on availability of your post still vacant

withdrawal of a resignation shall not be accepted where a Railway servant
resigns his service or post with a view to take up a private employment or in
a company wholly or substantially owned or controlled by the Government or
under a body controlled or financed by the Government; 

2) A person who had resigned may be re-employed in rare cases but the reemployment should be in the post or in the channel of promotion in which the
person was serving previously. The person concerned should be specifically
warned at the time of re-employment mat the appointment is entirely a fresh one
and that he is not entitled to any benefits or privileges of his past service.
Therefore, such persons should not be asked to refund settlement dues. It should
be clearly mentioned in the offer that the appointment is purely a temporary one
and that he should take his seniority with the other temporary / officiating
employees in the Grade. All such cases of re-employment should be approved by
an officer of at least Junior Administrative Grade

[E52 RC1/55/3 dated 14.03.1955]

If there was a technical resignation with a lien upon your resignation from the railway services then you may apply for rejoining the railways. 

Technical Resignation - Resignation submitted by the Railway employees on permanent absorption in PSUs is to be taken as Technical Resignation. ... The lien of a permanent Railway servant appointed under another Central /State Government or office may be retained on the Railway for a period of two years.

Retention of lien for appointment in another central government office! state government
A permanent Government servant appointed in another Central Government Department/Office/ State Government, has to resign from his parent department unless he reverts to that department within a period of 2 years, or 3
years in exceptional cases. An undertaking to abide by this condition may be taken from him at the time of forwarding of his application to other  departments / offices.

The exceptional cases may be when the Government servant is not confirmed in the department/office where he has joined within a period of 2 years. In such cases he may be permitted to retain the lien in the parent department! office for one more year. While granting such permission, a fresh undertaking similar to the one indicated above may be taken from the employee.

Firstly you have not acquired lien on the post due non completion of probation period if any. And if lien was acquired than this benefit is not available after resignation and acceptance.

Talk to management, what is their view on reinstatement. Further course of action can be decide on their response.

Now you might not have any other opportunity to join Railways again on the basis of your previous recruitment in case you wish to join the Railways again then you have to appear for the recruitment.

See since you resigned from the post you cannot go back and join. The withdrawal of resignation except in case of Technical Resignation is not permitted. 

Once your resignation is accepted by your appointing
authority, your name is struck off by the office and dues for your past services are cleared. You can no longer have any claim for the post you once held.

If the vacancy is available in that particular department and state government is relieving you from services.

- As per law, an employee cannot rejoin the same job ,once the resignation is accepted, because when the resignation is accepted , then there is no relation between employee and employer.

- It is up to the Railway service board to consider your case in extra ordinary cases.

- You can approach for the same to the higher management of Railway , after mentioning the situations in details.

- As per law, an employee cannot rejoin the same job ,once the resignation is accepted, because when the resignation is accepted , then there is no relation between employee and employer.

- It is up to the Railway service board to consider your case in extra ordinary cases.

- You can approach for the same to the higher management of Railway , after mentioning the situations in details.

No you cannot rejoin your post in railways.