Both rich_f and vempele are right, actually.
Basically, you use だとしたら in a hypothetical situation, usually hoping for advice and information if that situation were to occur. It's not a succession of events, but playing the field a bit. Even in that context it still doesn't make sense since it's just too hypothetical and seems unrelated to the result. You use だとしたら when asking people what they would think in a situation, or what advice they would give you if that were to happen, or what they would do if they were in your shoes. Subjunctive all the way.
ようでは is just a negative direct consequence; 'if X happens, then bad things will follow'. It's conditional.
Basically, you use だとしたら in a hypothetical situation, usually hoping for advice and information if that situation were to occur. It's not a succession of events, but playing the field a bit. Even in that context it still doesn't make sense since it's just too hypothetical and seems unrelated to the result. You use だとしたら when asking people what they would think in a situation, or what advice they would give you if that were to happen, or what they would do if they were in your shoes. Subjunctive all the way.
ようでは is just a negative direct consequence; 'if X happens, then bad things will follow'. It's conditional.