my Tree expert friend said:
As a general rule, trees don't like being brought inside. Iin bonsai, the rule of thumb is, for every day inside, a tree needs 5 days outside to recover.
The absolute worst time of year to bring a tree inside is winter. The tree (even conifers) will have gone into dormancy (or very slow 'tickover' metabolism) and bringing it into a warm, centrally heated (i.e. extremely dry) environment demands water from the leaves (or needles) that the roots can't supply because the tree is dormant.
Sometimes the warmth can trigger a false spring, in which case, the tree will begin growing and then putting it outside in freezing temperatures will kill it.
I say all this just to show that the odds are stacked against your mate. However, there are some things that can be done do to increase his (or her) odds.
1) Make sure the tree is properly potted. Many of these 'potted live' trees have just been ripped from the ground and have no useful roots to speak of. These trees will hold their needles for longer than cut trees, but will still invariably die.
2) Make sure it hasn't been sprayed with one of those 'anti needle-shedding' sprays (that stop christmas trees shedding all over the place). It's essentially a laquer that stick the needles to the tree but will clog the pores and will suffocate it.
3) Place it as far away from radiators or other sources of dry heat as possible.
4) Spray with a fine mist of water at least twice a day to keep up the humidity around the needles.
5) Don't let the soil in the pot dry out (aim to keep it damp, not wet).
6) Keep it inside for as short a time as possible.
7) When putting it out, don't put it straight out into a freezing frosty garden. Put it in a well lit but sheltered area (south facing wall), out of any harsh winds and protect it from hard freezing for the rest of that winter.
8) If it makes it that far, put it into prepared ground in early spring (late Feb. Early March).
So long and Thanks for all the Fish ;)