To borrow a phrase from another profession, "If you want three opinions on an antenna
, ask two radio techs".
Having said that, here is my two cents worth.
1. Assuming it is ONLY the tip of the HF whip that is damaged, cut it off and seal with sealant
of your choice. If it is a fibreglass former, then seal with fibreglass as first choice. The AT 120 tuner will take care of any slight change in electrical
length of the whip antenna
2. No, HF and VHF antennas can't be the same antenna. There is no real advantage in putting the HF antenna (assuming its a whip, not a long wire) on top of the mast and there would be significant technical difficulities in doing so.
As the VHF radio waves are propagated by line of sight, there is considerable advantage in having the VHF on the top of the mast. However, the HF waves are propagated differently (ground waves and sky waves etc) and therefore the antenna does not need to be so high.
3. Yes, leave the HF antenna where it is assuming it has been working OK in that location. There are other possibilities like a long wire backstay antenna etc but if it works, don't fix it.
4. VHF and 27 MHz antennas have to be different.
5. VSWR meter is not really necessary on the HF rig but is a "nice to have" option and certainly will allow you to troubleshoot antenna problems and perhaps get better performace out of the system if you take the effort to learn all the ins and outs of the mystical (and some say "black") arts of antenna theory.