The point of guided tissue regeneration is to recover lost alveolar (jaw) bone. The gum margin will generally stay where it is, the regeneration's objective is to reduce the pocket formed by the gum staying put and the jaw moving away down the tooth root. Hope that makes some sense.
Vertical bone loss is about as bad as horizontal, sometimes the vertical defect can be treated but often times it isn't detected until a lot of bone has been lost.
Ortho compromises bone only because it makes plaque removal more difficult, the process itself isn't an issue really.
Veneers are a bit less destructive of tooth tissue than crowns.
Mini implants are a relatively new development, they are intended as a cheap, short term solution, sometimes used alongside conventional implants to stabilise a denture while waiting for the standard implants to integrate with the jaw. As time has gone on, dentists have found that the minis are surviving quite well in the longer term, so there is a move to consider them a more permanent solution.
They can be used in places where there isn't enough decent bone for normal implants too. Not in children though.