As in the womb, so in life. The twins regard each other as simply part of the Way Things Are. They have been together since they were aware of anything at all.
The sole survivor, left alone when their monozygotic twin dies, is used to there being two.
As Julie Rae wrote in her poem, that introduces part one of Womb Twin survivors -The lost twin in the Dream of the Womb:
As I pushed throughDo you have a sense of being only half?
into this bright, noisy world alone
there should have been two
there should have been you...
I miss you.
Do you seek out a Best Friend to make you feel complete?
Do you feel stronger when there is somone else around who is very similar to you?
Do you always notice identical twins and feel a pang of longing?
If you do, you may be a monozygotic womb twin survivor and your twin is still, even years later, part of the Way Things Are.