charaNasmaraNAtsarvaduritasya vidAraNam |
sharaNam nR^iharim vande karuNAvaruNAlayam ||
As detailed elsewhere on this forum, even in the case of a mumUrShu, dasha dAnas are prescribed:
go-bhU-tila-hiraNyA-jya-vAso-dhAnya-guDAni cha |
raupyaM lavaNamityAhurdasha dAnAnyanukramAt ||
etAni dashadAnAni narANAM mR^ityujanmanoH |
kuryAdabhyudayArthaM tu prete.api hi paratra vai ||
dhenu dAna includes R^iNa, pApApanodana, mokSha, vaitaraNI and utkrAnti dhenus.
These dAnas should be given by the mumUrShu but can be given by the son or his representative as well:
bhUmishThaM pitaraM putro yadi dAnaM pradApayet |
These dAnas are considered to be of greater merit than even gayAshrAddha and hayamedha:
tadvishiShTaM gayAshrAddhAdashvamedhashatAdapi |
For Yogis blessed with siddha sa~Nkalpa, the best time for deha tyAga is also indicated:
shuklapakShe diva bhUmau ga~NgAyAM chottarAyaNe |
dhanyAstAta mariShyanti hR^idayasthe janArdane ||
dahanAdi samaskAras are not prescribed in the case of the death of a Yati and the pramANa for the same is below. I am surprised someone told you there was no shAshtra pramANa in this regard.
sarvasa~NganivR^ittasya dhyAnayogaratasya cha |
na tasya dahanaM kAryaM nAshauchaM nodakakriyA |
daNDagrahaNamAtreNa pretatvaM naiva gacChati ||
There is really no procedure for Atura sannyAsa. If there was time for procedures, what would be the need to take Atura sannyAsa?
AturANAM cha sannyAse na vidhirnaiva na kriyA |
praiShamAtraM samucchArya sannyAsaM tatra kArayet ||
AturaH here can be of two kinds: one on deathbed due to a disease or one in the face of death due to natural calamities, attack from a wild beast etc. Only under such circumstance can one assume Atura sannyAsa and skip procedures such as puruSha sUkta homa, virajA homa, upavAsa etc. Others, for the mere sake of convenience, cannot resort to Atura sannyAsa.
A Yati or Brahmachari is not engulfed by ashaucha in case of death. Here is the pramANa:
naiShThikAnAM vanasthAnAM yatInAM brahmachAriNAm |
nAshauchaM kIrtitaM sadbhiH patite cha tathA mR^ite ||
However, in the case of death of parents of pUrvAshrama, snAna is sufficient for shuddhi:
Na snAnamAcharedbhikShuH putrAdinidhane shrute |
mAtApitR^ikShayaM shrutvA snAtvA shuddhyati sAmbaraH ||
Similar is the prescription even in the case of Guru's death, for a Yati:
divaM gatau gurau shiShyaistadA kAryamupoShaNam |
snAtvA sachailaM yatibhireSha dharmaH sanAtanaH ||
It may be noted that a brahmachAri is free from ashaucha even in the event of death of parents, as long as he is not the one performing antya karma:
AdiShTI nodakaM kuryAdAvratasya samApanAt |
samApte tUdakaM datvA trirAtramashuchirbhavet ||
After the commencing of vivAha, yajna, vrata etc., if death occurs, there is no sUtaka.
vratayaj~navivAheShu shrAddhe home.archane jape |
Arabdhe sUtakaM na syAdanArabdhe tu sUtakam ||
Now what can be defined as the "beginning" of these activities? The shAstra states that clearly as well:
prArambho varaNam yaj~ne sa~Nkalpo vratasatrayoH |
nAndIshrAddhaM vivAhAdau shrAddhe pAkaparikriyA ||
Also, it must be noted, as kamalAkara points out, that ashaucha nivR^itti is only for the commenced karma and not for other karmas that one may plan to start during/after the started karma.
As stated earlier, there is no ashaucha in the case of the death of a yati. Here is another pramANa:
trayANAmAshramANAM cha kuryAddAhAdikAH kriyAH |
yateH ki~nchinna kartavyaM na chAnyeShAM karoti saH ||
bANena puShpadhanuShaH parikalpyamAna-
trANena bhaktamanasAM karuNAkareNa |
koNena komaladR^ishastava kAmakoTi
shoNena shoShaya shive mama shokasindhum ||