conditionals: future reference

I think that the grammatical rule that you are referring to, Bharat, is the one that states: when we want to talk about the future in a conditional way, the verb in the subordinate if-clause remains in the present tense and the verb in the main clause is in the future, normally will + infinitive. This is a very common pattern. Compare the following:

• If it's cold and wet next Saturday, I shall stay at home. I shan't be playing golf.
  ( NOT: If it will be cold and wet next Saturday, I shall stay at home.)
• If he doesn't let me know by tomorrow, I'm going to cross his name off the list.
  ( NOT: If he will not let me know by tomorrow, I'm going to cross his name off the list.)
• If I see Jane at the lecture tonight, I'll tell her you want to speak to her.
• If you want us to stay together, we'll have to show the world that we are responsible.

It is possible for the future will to occur in a subordinate clause, if it is reporting a question. Compare the following:

• Will you be seeing Jane at the lecture tonight?
  ~ I don't know / I'm not sure if I'll see her / she'll be there.
  But if I (do) see her, I'll tell her that you want to speak to her.

We can use do in the above sentence for contrastive emphasis, i.e.: It's not very likely that I'll see her, but if I do see her,…

conditionals: general condition

Note that if we are stating a general truth, the verb in both clauses normally remains in the present. This was probably Amy's intention, when she was talking about the things people need to do if they want to stay together. Compare the following:

• If I drink coffee in the evening I cannot sleep at night.
• You can walk on the grass if you want to.
• We prefer to sleep outside at night, if the temperature stays above 30 degrees.
• If you want us to stay together, we must demonstrate that we can keep this place tidy.
• If you want to learn a musical instrument, you must be prepared to practice for an hour each day.

Note that when stating a general truth, we can sometimes replace if with when or whenever:

• When I drink coffee in the evening I cannot sleep at night.
• We prefer to sleep outside at night, whenever the temperature stays above 30 degrees.
• When you are learning to play a musical instrument, you must practice for half an hour each day.
  

have got to / have to / must

Note that we've got to in your examples, Bharat, is not a reference to the present perfect. We've got to here is used as an alternative to we have to or we must to express obligation.

There is no difference in meaning and little difference in usage between must on the one hand and have (got) to on the other.

To some extent, must is used to talk about the emotions or wishes of the speaker or hearer, whilst have (got) to is used to discuss obligations that are imposed from outside by some external body. Compare the following:

• We must try to save some money, if we want to buy a house next year.
• Have I got to go to bed now? ~ Yes, you must, if you're going to get up early tomorrow to go fishing with Uncle Bill.
• Can you come skating with me tomorrow? ~ Sorry, I can't. I've got to work.
• Do you have to wear a suit to work, or can you wear casual clothes? ~ You have to wear a suit, I'm afraid.

Note also that past six months in your original sentence, Bharat, is a colloquial way of saying for longer than.

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