Traditional meads can tolerate storage in the 70s without much harm. Will it shorten their lifespan? Maybe, but they will certainly be able to last for years. They will probably darken more quickly. If you make a sweet mead, there is probably a higher risk that a spoilage organism will be able to grow and ruin a batch, though I haven't seen that happening (however, I sulfite them well).
For delicate melomels, storage at these temps will usually shorten their life dramatically. Even using plenty of sulfites won't stop them from taking on oxidized, Madeira-like qualities, or worse, cardboard-like character.