Army is going to stay neutral and would follow their duty according to constitution in words and spirit. Army would let the Parliament and President do what they can do to each other according to constitution. It means that army would not interfere as it did when Ishaq Khan dissolved the parliament of Nawaz. Even though Parliament was dissolved, at that time Army did not stayed neutral and non-interfering, as later they interfered on behalf of Nawaz, forcing Ishaq Khan to resign, even though constitutionally Ishaq Khan as President was supreme commander of forces (Army, Navy and Air force) and did what he was entitled to do constitutionally.
As it is constitutional right of Parliament to impeach President, President also have constitutional right to dissolve the Parliament. When President takes his constitutional step of dissolving parliament, President orders Armed forces to moves in and takes over whatever steps needed to secure the country, and army being neutral, obeys the command of President as their constitutional duty, Simple as that. So, let see what would happen and who would use what constitutional rights they have. It may take weeks for Parliament to impeach President but it takes only one minute for President to dissolve Parliament.