1. The surgeons decided to operate the patient at once.
2. I'd rather you will work hard next time.
3. It is about time he get married.
4. If he had not married,he would not have been a father now.

1. The surgeons decided to operate on the patient at once.
2. (Is any word missing?)
3. It is about time he get married.
4. Had he not married, he would not have been a father now.

__________________
The Me you have always known, the Me that's a stranger still.

it was about time he got married

1. Correct.
2. There is no need of any other word. 'Would rather that' expects a clause with past subjunctive mood.

I would rather that you worked hard next time.
[It is just a wish kind of sentence. You did not work hard in the past. Now wishing above for you.]

I think you were talking about the sentence like: I would rather eat homemade Pakoras than go to KFC for French fries. Lol]

3. It is about time he got married. (Again subjunctive)

Information: It's high time = It's about time.

4. Using the construction "Had he not..." does not make any difference. Both are tantamount to each other. Yeah, if you are concerned about the emphasis, that construction can be used.

Had he not married, he would not have been a father now.

Meaning, you are putting an emphasis on the clause by omitting if.
[By the way, I have noticed that these days DAWN newspaper is using such construction as above frequently. ]

Now, the real problem lies in the usage of 'married.'
Here, in this context, married is expected to be used as an object, not as the verb.

Had is expecting a verb. Therefore, the correct one is:
If he had not "gotten" married, he would not have been a father now.

Yeah, if you are following the British English, 'got' may be used instead of gotten. However, I would prefer gotten to got.

Information for readers: The above sentence is the perfect example of mixed conditional. Past -> present. How? The word 'now' in the sentence.

Regards.

Are you sure about the second sentence?
I'd rather that you "worked" hard next time!

110% sure!