The color changes are probably due to being in an active mating cycle. I've had many mysteries live then die but I've never seen one change color as it approached the end of its life.
On the other hand, the large size may indicate that your snail won't be with you for many happy years to come. Like you and me, they're small when young and large when older.
When they die it goes one of two ways: either they hang out of their shell and stink, so you'll smell it and remove it; or they'll slam their door shut (the foot at the bottom) and never move again. In the latter case, when given a nudge a month or two later the foot will float off, and dead dust, not smelly, will float out. Either way, no one else dies from their death, as 1-You remove it quickly, or 2-It's sealed.
All that active egg laying sounds more like a snail in its prime. What are you doing about the eggs? Do you hunt around the rim every morning and remove them? Does this snail have a mate, therefore the eggs are fertilized and you're aiming to have a snail farm?