For tragedy befalling a fellow believer, the other believers select from the following buffet menu of options:
1) They weren't actually as good as they seemed to be, but had committed some unknown sins in secret for which God is now punishing them. God punishes the evil-doer, even those who cover their sins from other humans.
2) They were good and hadn't committed any sins for which they're now being punished, but as the Bible says, "unforeseen events befall all".
Although the Bible informs us how and why evil came about, We know that God is all wise and all knowing and that He has reasons for allowing things to happen that are beyond our comprehension.
The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance.( 2 Peter 3:9
Men are slow in fulfilling their promises from various, often selfish, motives; the Lord's delay comes from love and long-suffering.
For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.(John 3:16)
It is essential to comprehend the difference between(1)unforeseen death and (2) judgement from God which is to perish with no future hope