So long as they are just standing there without any pressure on them or anything I've never really had a problem with prints warping or degrading over time. That said I had a spool holder that hung off the top of my printer frame that was printed in PLA and whole machine inside heated enclosure with the filament hanging on there and it warped and after a month or two dropped the filament eventually cause it had warped so much. So in the sun or under heat and or pressure over time the prints will deform but so long as they stay cool and aren't supporting weight they'll keep their shape for a long long time.