We need more info on your combo you plan on running, i.e. motor only, boost, n2o. It all depends on your combo and the size of your stroke (no pun intended). Things like nitrous, heavy abuse, compression, boost, etc..etc.. will all come into play in its life expectancy.
With timely up-keep, that motor should easily last 50 thousand miles before it starts getting tired. With a 542 stroker and nitrous, you'll be breakin parts long before you wear out that short block.
Depends on who's building it and how much power adder you plan to add to it. A well built stroker motor with no power adder should last as long or longer than any factory motor. An occassional shot of gas up to a 150 shot should not diminish the life much. A big direct port shot of NOS or 2-stage NOS, well who knows?