Some thoughts...
Even if you never need your "get home" engine, having one adds peace of mind.
Sometimes peace of mind is all that separates folks that set forth, and folks that stay in port.
My questions about "get home" engines don't represent being comfortable with not having a second engine. I'm not convinced a "get home" engine in the 25 hp range can be an effective "get home" tool on an Atlantic crossing. However, it may well be effective in holding course while repairs are being made on the main engine. For that reason they may be valuable. So it might be better than not having one.
I'd say when it comes to such crossings, people fall into three distinct groups.
Group 1 would never cross in a private recreational vessel of any sort.
Group 2 would cross single handing, with a single engine and in relatively small boats, power or sail. These are adventurers and to others either brave or foolhardy or some combination of the two.
Group 3 would cross the Atlantic but would only do so in a larger boat, perhaps only with twin engines, and only with a larger crew rather than just one person.
While I respect the right of various boat owners to do as they wish and recognize that many have crossed single handed and some of those in extremely small boats (even under 20') of very questionable capability and others somewhere in between, I personally fit solidly in Group 3. I don't argue that it's the only way, but it's the only way I'd be comfortable. Now, I have very little problem with the idea of crossing with a single engine, although I want twins. Well maintained with a good capable crew, a single is acceptable even if not my preferred choice. However, the idea of crossing single handed, of sleeping while operating a boat and of not having a second person in the case of problems is not something I can personally gain any sense of comfort with. Menzies referenced MV Dirona in this thread. I read several of the "Nordhavn" posts on my flight today, including Gales, Steering Issue, and Alarms at 1:15 AM. I'm not saying one person wouldn't have made it, but their handling of those situations was very dependent on two capable persons aboard. Now, I even go a step further. It's pleasure boating for me and that doesn't mean days with inadequate sleep. I absolutely wouldn't cross single handed, but I personally wouldn't with only two people. My minimum crew would be three. My personal opinion, and everyone is entitled to their own, is that one person is dangerous and only two is just outside my definition of pleasure.