Etiquettes

Replying to salaam correctly

Q: A known person to me sometimes greet me as Assamualekum without la in it, clearly. Sometimes I reply to him in forgetfulness Walekum assalam, instead of Walekum. Then I realize that, and don't know what to read as a counteract to that. Could you please tell me what to do at that times?

Saying "Khuda Haafiz"

Q: What is the ruling regarding saying "Khuda Haafiz" when departing from a meeting? I know that it is best to say "Assalamu Alaykum", but since "Khuda Haafiz" also has a good meaning, would it at least be better than saying "Goodbye"?

Replying to the Salaam

Q: Is it obligatory on us to reply if anyone says to us Assalamu Alaikum Wa Rahmatullahi Wa Baraakatuhu? What will be the extent of that reply, do we have to say Wa Alaikum Assalam Wa Rahmatullahi Wa Baraakatuhu or we can just say Wa Alaikum Assalam? Whenever I receives your reply through email, there is always written Salaam in the beginning, do I have to reply to that Salaam as well?