Some Priests will not do absolutions at adoration. What if someone’s in mortal sin and they need forgiveness? If the priest says not during adoration and something happens and they die are they covered?
Probably yes. It depends on their contrition

The tridentine catechism reminds us (I quote or paraphrase below):
<<By the Fathers of the Council of Trent, contrition is defined: A sorrow and detestation for sin committed, with a purpose of sinning no more. and a little further on the Council, speaking of the motion of the will to contrition, adds: If joined with a confidence in the mercy of God and an earnest desire of per forming whatever is necessary to the proper reception of the Sacrament, it thus prepares us for the remission of sin.
[T]hrough perfect contrition, accompanied by the desire of confession, God remits the sin of the penitent.
Perfect contrition is an act of charity, emanating from what is called filial fear. Sorrow for sins committed should be so profound and supreme that no greater sorrow could be thought of. Besides, our contrition should be not only the greatest, but also the most intense, and so perfect that it excludes all apathy and indifference. It must also be equally extended to each mortal sin.
Perfect contrition must include detestation of sin, intention of confession and satisfaction, and a fixed and firm purpose of amendment of life.
Such is the efficacy of true contrition, of which we have spoken above, that through it we obtain from the Lord the immediate pardon of all sins.>>
The more recent catechism summarizes contrition as follows:
<< When it arises from a love by which God is loved above all else, contrition is called “perfect” (contrition of charity). Such contrition remits venial sins; it also obtains forgiveness of mortal sins if it includes the firm resolution to have recourse to sacramental confession as soon as possible.
The contrition called “imperfect” (or “attrition”) is also a gift of God, a prompting of the Holy Spirit. It is born of the consideration of sin’s ugliness or the fear of eternal damnation and the other penalties threatening the sinner (contrition of fear). Such a stirring of conscience can initiate an interior process which, under the prompting of grace, will be brought to completion by sacramental absolution. By itself however, imperfect contrition cannot obtain the forgiveness of grave sins.>>
If you have true, perfect contrition in your heart and you cannot confess for whatever reason, you may have in your heart a founded hope that the Lord may have remitted your mortal sins. This is because part of perfect contrition is the firm intention to confess as soon as possible. If the penitent were to die (which of course, would have been foreseen by the good Lord), he would have a firm hope of dying in the state of grace and in friendship with God.
Always ask God for the grace of perfect contrition. Ask for Our Lady’s intercession. She was at the foot of the Cross, and now she too lives in heaven with the Lord. She understands better than anyone what you need.