It's never a precise math due to other considerations (tax breaks, product placements, merchandising, after sales markets, royalties to actors/authors if applicable etc) but a WW gross of roughly double the budget (including marketing costs which are not always disclosed as part of that budget) is considered a near enough 'best guess' guide for a theatrical run break even target.
Anything above that and what comes from the after sales markets is all profit (subject to taxes of course). As some marketing costs are not disclosed when I see that I think it's maybe a bit more accurate to say 'double and add another $50mil', depending on how many TV spots an so on there have been (TASM2's marketing costs for example are thought to have been huge).
So yes, 'Terminator: Salvation' did indeed underperform on it's theatrical run, but that I think was simply down to it not being very good at all than the concept being worn out/audiences bored with it. In the longer term with after sales and so on it likely made a small overall profit, but not enough for them to continue the series where T4 left off: They are effectively stealth rebooting the franchise ala Star Trek/DOFP style time travel shenanigans in 'Genesis', and the return of Arnold.
As Donut said: its 'The return of Terminator'. As in Arnold, in person, rather than a CGi face cameo.
Will it do well? Hard to say... Arnies return is a big plus for fans of the franchise, and it going back to it's beginnings with Sarah & Kyle too add another factor of interest for me, but in the end if the story is a load of crap I wouldn't expect wonders. If the story is good though I could see it doing very well and ought to do better than this FF reboot.
