If you have a mobile phone that's compatible for use in HK, you might want to provide CX with that number and better yet, do it yourself & set up flight alert/local paging or update in case of a delay, connection change, etc. - CX's system will do a SMS alert ahead of your departure from HKIA and you can relax & enjoy the sights, sounds & dinner with your friends in town.

MTR's subway system (including the Airport Express) is very reliable (98.5% or better) so I wouldn't worry about delays - the taxi ride back to HKG is more expensive & a little slower but the trip on that "motorway" is usually free of delays or traffic tie-ups in the late hours of the evening.

The bus from the HK Station to the peak is very scenic, winding its way up the hills but will take 30+ minutes as it make stops along the way (more like 45 minutes as I recall depending on local street traffic as you will be in the middle of evening rush hours going up) whereas the taxi will be quicker, at perhaps 15 minutes. I would let the local friends/hosts take care of and plan the logistics on where to, etc.

If they are truely locals living there for a while, they probably can even show & ride with you - after dinner - coming down the peak on those mini buses (15 pax) that are fairly quick & inexpensive (it's like $1.25 USD one-way) and will drop you off at the Central MTR station, where you can make your way back to HKIA for your departing flight.

If you opt to stay on the Kowloon side & exit the Stations, there are plenty of excellent restaurants within 5 to 10 minutes walking distance, plus the IC Hotel on the waterfront for seeing the Victoria Harbour at night (and the free laser show) while enjoy dinner and/or cocktails - and walk pass the busy & crowded Nathan Road and the shops on the way back to catch the express train.