No. As stated on page 184, you cannot remove a model from a unit of Skirmishers if doing so would cause the unit to lose coherency. However, if an attack targets a specific model (such as a champion or a character), that model must be removed if the attack reduces it to zero Wounds. In such cases, simply replace the removed model with another model belonging to the same unit, one that could be removed as a casualty, in order to maintain unit coherency.

The centre is the point that is equally distant from the models at the extremities of the group. However, when considering blast templates, the purpose of placing a blast template over the centre of a unit is to ensure a significant number of models are underneath it. In the case of a unit of Skirmishers, this is not always possible. Therefore, you may place the central hole of a blast template over the model closest to the centre of a unit of Skirmishers.

The unit loses coherency, as described on page 184. This means models belonging to the unit must be removed from play as casualties until the unit becomes coherent.