failure on HF happens sometimes despite your best efforts. The more experience you get the fewer failures but I had a complete failure last week on VP8/EF-014. With a few exceptions I have gone back and had a successful activation, but I suspect VP8/EF-014 is not going to be one of them.
Sometimes 5watts from an FT817 doesn't make it, but they are reliable and I have had over 600 activations from one. Activating later in the day sometimes helps, avoiding an early start, but make sure you are off the hill before it gets too dark, and carry a second torch!
I would not put all my antenna eggs in one basket! A linked dipole is a good idea but I have had breakages from high winds and poor maintenance (I know I should check my kit more often). Having a second dipole in case of a breakage is a good policy, but more hassle changing between them. I only use resonant antennae saves the weight of a tuner.