Almost never - remember the regional management is being squeezed hard by their customers, the legacies, to provide lift as cheap as possible. While training new hires is expensive, they're not exactly over-paid either. A regional that tries to build a long term stable career path eventully runs into a expense issue that kills them - see Comair.
Nobody should be looking at a regional airline as a career, the primary reasons for which is your management doesn't want you there as a career pilot, so if that's your goal already you're at odds with the people who control much of your work environment.
Plus - working at many other places is better - a regional will NEVER be able to provide the kind of working conditions and pay that you can get at a legacy or even an LCC. You can't retain people, or at least you can only retain those verging on the insane, so kiss them goodbye and ramp up the hiring machine.
The current short term crisis is that with stagnation in the industry for so long the pipeline of freight and "academy" pilots to fill those right seats is a little short - but trust me, it'll pick right up in the next 6 months and the supply of 250 hour wonders will be just fine. Until age 65 kicks in and we all have to sit in the seat we're in for 5 years until that works itself out.
