Youll lose the satellite controls and the part of the display which shows radio station etc. However, the clock and the temp. display will stay.
When you disconnect the original Renault stereo, youll see 3 plugs - 1 black, 1 clear, 1 yellow. The black one carries all the power, light etc, the clear one connects the speakers to the head unit. The yellow plug, a small square, will not fit into the new Pioneer unit - thats the one which has the remote and the display.
Sinply fit the black and the clear plugs into the lead you get with the head unit, then connect the black plug at the end of that into the back of the head unit.
BTW, youll need to buy an antenna adaptor, as the standard Renault one is female, and youll need a male to go into the Pioneer.
Hope that helps.