All the content of C2 began life as either an orphan page or a page someone added to an orphan page.
Therefore,
Don't delete pages just because they're orphans - doing that is like a farmer eating their own seed stock.
Orphaned pages do no one any harm. Let them be and you never know which ones will one day spring to life, probably at the hands of people who aren't even on c2 yet.
But,
Inactive orphans with no relevant content are prime candidates for deletion. They may not do any harm, but it also does no harm to delete them. Of course, don't delete orphans just because they are orphans.
Before you delete it, think about SavingOrphans:
There are different reasons that pages are orphans.
Do not fear, that if you do not delete/refactor them now, you cannot find them later. OrphanPages will list them. And earlier or later they will turn up in RandomPages and somebody will take care of them. I regularly check RandomPages for interesting tidbits. If I stumble over an orphan, I delete it (or mark it as such) as often as not (see also RediscoveringOldPages).
And it's always fun to exercise the extent of your WikiMentalMap? by seeing into how many relevant pages you can work an OrphanPage's name.