yes, there are chances for failures. Because virtual machines can be powered on even if there are not enough resources to ensure failover capacity. When this is done, no warnings are presented, and the cluster does not turn red.
Upto an extent we can avoid it by enabling "Admission Control" in HA.
In general, using VMware HA strict admission control ensures that you cannot power on a virtual machine if doing so would violate availability constraints (in other words, cause the current failover level to become less than the configured failover level). When such an attempt is made, a message informs you that the virtual machine cannot be powered on.