With those assumptions (especially modal realism), I don't think your original statement that our simulation was not terminated this time doesn't quite make sense; there could be a bajillion simulations identical to this, and even if most of them we're shut down, we wouldn't notice anything.
In fact, I'm not sure what saying "we are in a simulation" or "we are not in a simulation" exactly means.
What you say is like quantum immortality for many simulation world. Lets name it "simulation immortality" as there is nothing quantum about it. I think that it may be true. But it requires two conditions: many simulations and identity problem solution (is a copy of me in remote part of the universe is me.) I wrote about it here: http://lesswrong.com/lw/n7u/the_map_of_quantum_big_world_immortality/
Simulation immortality precisely neutralise risks of the simulation been shut down. But if we agree with quantum immortality logic, it works even broade...
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