1999 water pump/timing gear question

We have a 99 Intrepid, with 106K on it. Bought it 2 yrs ago for my wife on short notice when her other car(neon) was destroyed by a drunk driver. Iy has a 2.7 in it, only problem is a small amout of smoke we see once in a while, and a/c is now non working for some reason. It had 101K on it when we bought it, so she drives it very little. Use Mobil 1 in it, no sludge I can see. My questions are - since the water pump in internal, what does it do when starting to fail? Does it leak or just break? Will it leak only internally, or externally as well? Does it make noise most of the time or what are any other common signs? I know from threads it can cause chain to jump and destoy engine, just want to see if I can see any obvious signs before this happens. Also, is it critical to change the chain at 100K? I see some folks mention this as a prevention along with pump at 100K, but sure is an expensive venture from what i see. Lastly, any way to tell if this has already been done by previous owner? I know this question may be a stupid one, just do not know how to get hold of any previous owners. Would have asked this before I bought it if I knew ahead of time.