Arjun should show up at party because only Mnav and may be Archna can convince Purvi to come back to job even for a few days. Otherwise it will be hard for Arjun to make Purvi agree to come back to the office.
The condition, argument that took place was between Arjun and Purvi they need to sort it out. Manav/Archana can talk to them make them understand state his point of view but final decision will be on them. Arjun wants to prove that his company doesn't need Purvi then why would he offer her her job back? Even if he does why would Purvi accept it? Probably hence the serving period was brought up.