With Hybrid Swordmages, you only get the Aegis once per encounter, but you can regain it by dropping the marked enemy to 0. What if you mark using Total Aegis or Double Aegis, though? Do you have to drop all affected enemies to regain the Aegis?
You regain your Aegis if any target is dropped or loses its mark
The Double Aegis and Total Aegis feats were presented in the same book as the Swordmage class, and thus obviously predate the Hybrid Swordmage entry. The wording of the Swordmage Aegis (Hybrid) feature says "you regain the use of [your Aegis] when its target drops to 0 hit points or when its mark is superseded by another mark." All creatures marked by your Aegis are targets of it, and no special instructions are given for if there is more than one target (such as saying "all targets" and "all marks"), so dropping any target or overwriting any of the marks with another should recharge your Aegis.
Do note that the previous restrictions still apply, so if you use your Aegis while you still have targets marked with it, the old marks will disappear.