The reasons behind a trade really have nothing to do with judging the results of the trade. Now one can consider the money saved in the trade ($40 million) but that is actually balanced somewhat by the money paid to Segura ($60 million over 4 years).
Bottom line is you just can't judge the trade on shortstops. Plus 4 years of Segura at $60 million is probably not going to be as valuable as 6 years of Crawford at maybe $20 million total (if it is more than that the Seattle is winning the deal big time).
If we had Crawford and Santana we would have had many options as well. Other places to trade Santana. Play Santana at 3B and live with the defense. Flip him for a $20 million starter. Sign McCutchen and play them both (hey we know we don't care about defense).
Bottom line is when all is said and done it is very unlikely that the Phillies win this trade. We are definitely not winning it this year with Santana. Next year might be 50-50 on the shortstops alone. Basically this was going to be a good trade for the Phillies only if Segura helped them win now (which he isn't) or if Crawford failed (which he does not appear to be doing). It probably will end up as a truly awful trade for the franchise.