The Forever Building

Have You Ever Wondered How They Can Consider A Mausoleum A Place To Last Forever? Back In The Bible Days A Tomb Made Sense Because It Was All Rock. However The Modern Day Mausoleum Is A Building With A Roof. Yet They Entomb People Inside For Eternity. How Can That Be?
Both My Parents Will Be Placed Inside A Mausoleum. It Makes Me Wonder When This Building Will Reach A Point In Time Where It's No Longer Considered Inhabitable. I Have Yet To See A Building That Was Made To Last Forever. I Suppose I Won't Be Around When That Happens. I Am More Curious Than Anything. Your Thoughts?