S. R. Faruqi:

kasaalaa khe;Nchnaa = to endure hardship
salmah-e all;aah ta((aal;aa = may God Most High keep someone well

In this 'ground' and meter Sauda too has well versified salmah all;aah ta((aal;aa :

mai;N dushman-e jaa;N ;Dhuu;N;D ke apnaa jo nikaalaa
so ;ha.zrat-e dil salmah all;aah ta((aal;aa

[when I searched for and dragged out my mortal enemy--
well, Your Excellency the Heart, may God the Most High keep you well!]

But in Mir's verse there's an additional pleasure-- the heart has already arrived near ruin/destruction, and the speaker is giving it the blessing, 'may God keep it well'. Thus in it there are two kinds of sarcasm. One is that he's giving the one who is about to die a blessing of remaining well; and the other is that usually people give the blessing of remaining steadfast/unmoved under hardship and difficulties to those who would be very dear, or through whom the blessing-giver would obtain benefit, or whom the blessing-giver would revere. In this regard too, that wretched heart, which while enduring hardship after hardship has drawn near to death's door-- to give it this blessing is very fine.

Nazir Akbarabadi too has composed a ghazal in this ground, and has also used this phrase:

kyaa jaani))e kis ;haal me;N hovegaa ((aziizo
dill aaj miraa salmah all;aah ta((aal;aa

[no telling in what state it will be, my dear ones--
today, my heart-- may God the Most High keep it well!]

Jur'at too has composed a 'double-ghazal' [do-;Gazlah] in this ground. And in the opening-verse of the first ghazal, and in the closing-verse of the second ghazal, he has included salmah all;aah ta((aal;aa . In the closing-verse, he has created a pleasure by mentioning the love of idols. In the closing-verse, contrary to Sauda, Mir, and Nazir, he hasn't versified the theme of the 'heart'; rather, he's carved out a new path:

jur'at se bhii ((aashiq nahii;N hote kih shab-o-roz
hai ma;hv-e butaa;N-- salmah all;aah ta((aal;aa

[there aren't any lovers like Jur'at-- who, night and day,
is absorbed in idols-- may God the Most High keep him well!]

It's undeniable that Jur'at's theme is trifling, and his tone is only a jesting one, whereas in Sauda's and Mir's verses there's a 'mood' of sarcasm and bitter-sweetness. Jur'at's verse is, nevertheless, better than Nazir's. And for his absorption in idols to be blessed with 'may God the Most High keep him well'-- it's very enjoyable.

FWP:

SETS
MOTIFS
NAMES
TERMS == DOUBLE-GHAZAL; GROUND

Another possibility: the speaker might be recognizing that with the destruction of his heart he himself is near death, so that he might be giving a last, final farewell blessing to the friend who is the addressee: 'May the same thing not happen to you!'. It's less piquant perhaps, but it avoids the awkwardness of having the speaker personify his own heart and address it as yaar . But in any case the whole verse is basically a vehicle for making clever use of a common blessing-- one that is long and complex enough so that to 'seat' it so nicely in a short meter is an enjoyable feat in itself.

Note for meter fans: In the first line pahu;Nchaa has to be scanned long-short. Thus pahu;N has to be scanned as one long syllable, as though it were phu;N .