I instructed on PA39s completing about 500 hours of training including many flying asymmetric and there was never a problem on one engine although, as is typical with many light twins of this ilk, the rate/angle of climb wasn't too sparkling.
I realise the PA30 may well be a different breed (I did a few hours on them also) but as far as I can recollect the only significant difference was that the props on the PA39 were "counter revolution" hence there was no critical engine which on the PA30 there is.
That said, from the evidence we have so far, it would seem that if this was an engine failure it happened in the cruise rather than just after take off. Assuming the engine failure was handled correctly and the prop feathered this would allow some time to declare an emergency etc.