Is there any evidence that whoever earns an unlawful livelihood will return it before their death, whether it be from fornication, falsifying certificates, or other tangible and intangible matters? And will Allah strip a person of some blessings before their death as a recompense for them?

Sins remove blessings and bring about retribution. No blessing has ever been removed, nor has retribution ever befallen, except due to a sin, as Allah the Almighty says: ﴿And whatever strikes you of disaster - it is because of what your hands have earned.﴾ Allah does not change His blessings until the servant changes what is within himself from obedience to disobedience, or from gratitude to ingratitude, or from causes of contentment to causes of displeasure. Recompense is of the same nature as the deed. So, whoever changes sin to obedience, Allah will change punishment to well-being for him.