When you get to the screen where you pick a bonus for next map, try clicking on a map area, there are 2 areas available after 1st dragon slayer map...
There are several occasion of where you can pick a map to play, Even in RoE campaigns( you could pick which map to play first barbarians or swamdwellers, and in other campaign you can pick to play firstly with inferno or dungeon), AB first campaigns, at some time in SoD campaigns... yet many people don't realize this option even after spending years with the game
And about your situation, you wont get the crown, since the pendant will be on your next map
![:P :P](/forums/images/smilies/p.gif)
But as a bonus for going through campaign in this order you have chosen, you will get access to bonus area on next map, if you get collar of conjuring or something from rust dragon map.. and if memory serves, that bonus area contains one cloud castle, one naga dwelling + some artifact..
I still prefer going the other way around, since those dwellings are not worth it, having crown in 4th mission is better imho, especialy since there is .... significant mana problem on 4th map.