Hi KangaDR, welcome to CDI!
Very quick answers to your questions:
1) Probably yes, but it's unlikely to be cost effective. Also, the halo seems to be pink.. which I take not to be the case with your current ring.
2) This is really a question that you want to ask David (the owner of DBL) when you discuss what you would like as a replacement, but in any case the majority of the value of your current ring is likely to be the centre stone, and now that is seriously damaged. Also, engagement/wedding rings have limited demand on the "second hand" market.
3) Yes and no. You shouldn't feel constrained to a specific pre-made ring, but at the same time, particularly with coloured diamonds (which are mostly not-round and not cut to standard proportions) it makes sense to have the setting made to fit at the same time as you purchase the centre stone.
4) Generally yes, but see 3) above. And a properly custom-made setting does not need to be hugely more expensive than a stock-made "standard" setting.
5) Heh. That's the $100,000,000 question. I just bought a couple of books on coloured diamonds from the mid/late 1990's and they refer to "the last couple of decades (1970's on) seeing a significant increase in the interest and prices of fancy colour diamonds". 20 years on, and the trend hasn't changed. Can it change tomorrow? Yes - in fact I'm surprised by the way in which prices have moved during the 2008-2010 recession. Will it change tomorrow? Unlikely; differently from colourless diamonds, true "fancy colour" diamonds are actually rare, not just exploiting commercial restrictions and a lot of marketing. However, predicting fashion is an impossible task, and any claim of rarity (which BTW applies to the best stones, not all!) is worthless in the absence of demand: my oil paintings are extremely rare, but no-one wants one even for free, never mind being willing to spend money for it.
Hope this helps - I'm going to sleep now, so further replies will come from others or in a few hours, but please post back if you want to continue the discussion/ask more questions.