Yes they do and even if the percentage is small, that is just fine with me. If you can keep your scenarios always having a positive balance at the end it is a good plan, regardless of percentage remaining. I want to assure we or my surving spouse do not run out of money.
See answer number 1.
You are correct, the big picture should contain many more factors then just the ending balance. In one of my early plans I would start my pension at age 63 and Social Security at age 68. I did this in light of aligning my Roth conversions to max out the 12%/15% bracket. In a later plan I noticed at age 71 my RMD along with my Social Security and Pension were fully supporting our living expenses, which also had the unintended consequence of minimizing the amount of Roth conversions I could do while keeping within the 12%/15% tax bracket. In studying a solution for this I realized if I delayed starting my pension from 63 until 65 and delayed starting my social security from 68 to 70 I could increase the amount of my Roth conversions between age 62 and 70, before the RMD kicks in, which also helped reduce the RMD amount and the associated taxes. Further as part of this step I realized it is better for us to live off of our existing Roth accounts during these intervening years in order to maximize IRA distributions and keep them maxed at the 12% bracket.
Another deciding factor was that by maxing out the Roth conversions I was minimizing the remaining IRA balance and reducing the inheritance taxes our daughter would have to pay on the inherited IRA. This plan has been working will for several years now and has the added benefit when the just passed "SecureAct" hit that causes the loss of the inherited stretch IRA's, it turns out my plan in minimizing the inherited IRA balance is spot on and my daughter still will be better off with reduced IRA taxes, even though she has draw down the inherited Roth within ten years.
Regardless of my annual cash flow needs, pre-Pension and pre-Social Security, I max out my Roth Conversions as it allows my to pay the lowest marginal tax rate. Then I withdraw annual income, as needed, from the Roth account. As far as cash needed to pay for the Roth conversion taxes for the first two years of retirement it came from the taxable account, but as that was spent down I now pay for it out the Roth Distributions I take for annual income. This is contrary to what some use as the "wise tale rule of thumb" that you can only do Roth Conversions if you have separate cash to pay the taxes. That it a misconception, If I did not do a Roth Conversion, and just took IRA Distributions for annual income, where is the cash coming from to pay the taxes on that? You can see I'm paying the exact same taxes on the money, regardless whether the 1099-R says "IRA Distribution" or "Roth Conversion", same balance, same taxes due.