How to calculate battery life
My calculation, probably missing something, but here's what I did:

$$
1 \mathrm{\ \mu A} + (50 \mathrm{\ mA} \times 0.1\%) + 25 \mathrm{\ \mu A} =
76 \mathrm{\ \mu A}
$$

$$
\frac{76 \mathrm{\ \mu A}}{  80 \, \% \mbox{ efficiency}} = 88 \mathrm{\ \mu A}
$$

Round up to \$100 \mathrm{\ \mu A} = 0.1 \mathrm{\ mA}\$

$$
\frac{2700 \mathrm{\ mAh}}{  0.1 \mathrm{\ mA}} \approx 3 \mbox{ years}
$$

If you're using rechargeable batteries, they'll discharge on their own long before that. Or if any of your other calculations are off (like maybe it's a 98% instead of 99.9% sleep), that will affect it a lot too.