1. You can give Power of Attorney in favour of person in India whom you can be entrusted upon. You can execute it there & get the same apostille from Indian Embassy.
2. It is advisable to stay in loop and accept NEFT transfers against purchase consideration into your account.
3. If the buyer agrees to buy your property & can't wait until you return then for securing your rights into the property and your security into the sale consideration of it, it is advisable for you to ask for 10% of earnest money deposit and 40% of sale consideration paid to you in advance before taking possession. Also be very specific on terms of rest of 50% of the sale consideration by the time you return to India, so that once you are back you can execute the sale deed.
4. Make sure that such an agreement to sell is registered document with sub registrar of the vicinity where the property is located. This will help you to make such document enforceable if in any case the purchaser fails to pay you the rest of the sale consideration.
5. Make sure two important clauses are incorporated into the agreement to sell:
One, that the purchaser agrees to evacuate the property within a month from the date he fails to pay the arrears of sale consideration and the vendor may refund the sale consideration paid earlier after deducting registration and clerical cost incurred borne by him.
Second, that it shall be sole prerogative of the vendor to sell the scheduled property to any third party if the purchaser fails to fructify obligations mentioned in this agreement to sell for consecutively three months/three installments.
This perhaps suffices your requirements in query mentioned above